lookslike fenixp is fellow space marine :)
I am sorry that I haven't specified what T1 means, thx for updating it. Regarding BO of marines, i am playing mostly with friend together and marines before comander suits me well, but on other hand, building comander first is good defence to early enemy rush, but in singleplayer it is not important. In the end it is better to stick with fenixp's advice - comander and then your army.
plasma vs HB
plasma - great against heavy armor, weak against light armor, short range, shoot while moving, lower damage than HB, better accuracy
HB - good against anything, long range, high rate of fire, low accuracy (good with target finder upgrades) high damage, delay for deployement.
Personaly, i prefer plasma due to lack of deploy-delay, so i know what can plasma do :)
regarding stun, what i know it is about 25% as you said, but i haven't found anything more on gamemechanics of this.

Nah, I'm Imperial Guard now, I was playing SM far too long :D
When struck, the following effects may be triggered on the target
3% chance to disable abilities for 4 s.
3% chance to disable movement for 4 s.
20% chance to disable combat abilities for 4 s.
[url=http://wiki.reliccommunity.com/Assault_Terminator_Squad_(Dark_Crusade)]relic wiki[/url]
(why do we Czechs have always have to be the biggest freaks regarding this kind of stuff? :D)

How about a new national motto: "The Czech Republic: Game Accountants Since 1993"?

it is maybe genetical that we need to know all about game mechanics :) and thx for this info on stun.

The problem I am having with enemy bases is finding the damn things. Th AI finds mine a whole lot faster than I find its base. Also, by the time I do find its base (if I am lucky) I have units coming at MY base from three different directions. It wouldn't be so bad if I didn't have to wait for a sizeable enough force to go scouting. If I take just the commander and honor guard I run into a horde of infantry well before the base or they find mine and then I'm stuck in vomit-out-troops mode until I get pissed off and quit. I don't mind a challenge but something's got to give here.
To everyone who has replied, thanks for the advice. I can trounce Chaos even before I bring out the big guns. Tau I had no problem with. Orks I never encountered because the Necrons killed them(along with everything else). Still hate the Eldar and Necrons. Tried plasma on them but they eat me with zerg rushes before I can get enough plasma on them. Heavy bolters do OK but I can't tell while being ripped to shreds. I have been trying my best to follow the tactics you all have suggested and they work but this game......hmmm it's something else heh. I think I will shelf this one and try some of the other expacs. Sorry for the bitching, but that's what my frustration at this point has got me doing.
To clarify, I am playing the single player campaign not the skirmish option in the game's menu.

this game is easy to learn hard to master, try playing on easy to learn basic strategies and weaknesses of your enemy, it took me some time to be able playing on normal and i have still problems on hard :)

i played this game for about 50hours plus (i used alot before i used xfire !!!) the best tactic is to send expenderble unit to scout out corners of the map preerbly units with infiltrate ability

There's usually 8 roughly equidistant spots around the maps for bases and you always occupy one of them. On large maps I make a pair of scouts and send them to the diagonally opposite corners from my base and then have them converge on the exact opposite side of the map to my base. Most of the time they'll find the enemy by the time they meet. If you load up the skirmish interface, you can have a look at the maps the game uses and get an idea roughly where spawn points are. Sure its sort of cheating but I think it's also sort of cheating to have a battle barge in orbit and not be able to ask them where the enemy are...
Probably the most important thing (at least I think so) is that I don't let the scouts retreat if they get in a fight, I'm not sure if the AI is designed to take retreat direction into account when scouting, if it scouts at radom or, more likely, it knows where you are from the start and just delays finding you to give you a chance but I avoid letting it follow my scouts back to base.

I have concluded that in this iteration of the series the computer is a cheating bastard. So I am currently working on becoming a cheating bastard to counter the bastardliness of the AI.

Part of the problem with some RTS games is that the human is limited by the interface the methods of input, such as the mouse and keyboard combo. Now, if a human being could access the game in the way the AI does then it could be interesting....but then they might not be something we would consider human....

In single player you can actually pause the game using spacebar I think it is. This is handy if you have alot of micromanagement to do in a large battle. You can give all the units orders and reinforce/rearm squads and sort your base out. Its handy while learning the game to give you time to think about what you would like to do, later if you play enough it becomes instinctual so you wont need to pause to pull off the same results.

Yep, AI cheats like hell, more resource income, I think even faster build times... But it's still possible to beat it (not to mention there's a non-chating computer patch lying somewhere around the internets - but it's even harder to beat it then, cause it improves AI :D ). But it's still possible to beat it, just requires some training - I'd reccomend you playing a few skirmish battles against harder and harder opponents, it's still fun and you'll learn to play true Dawn of War (even on normal campaign, your units have more HP and maybe even damage than in MP or Skirmish)

A neural link would make it an even battle (despite feeling a bit Beneath A Steel Sky, probably have to go to that body modding clinic) but so would coding a delay into commands to simulate the actual interface. Even if they timed a guy with uber-micro then it'd still be far slower than the computer can work.

I am going to buy OCZ Neural inerface actuator so I will tell you how it feels to fight AI with your brain ;)