Example.
I'm In Junktown and decided to just go kill the skulz gang myself. Now I see a walkthrough and it says to do this and that and this and that. I've killed Vinnie and all. Did I destroy the story? Is the mission impossible now? Can I just go on klling sprees and still finish the main story?
Thank you. :)

as long as you get them a water chip, and then get the final objective, you're fine.

do a search for fallout 1 speed run on youtube if you really want to know how linear it is.

There's very few required items to finish the game, and it's nearly impossible to brake the plot in play. It is possible to lose the game, but that is unlikely to happen in play.
Oh, yeah, just to make it clear: Killing the Skulz gang doesn't break the plot. Nor dose killing everyone in Junktown, if you really want to make a bunch of corpses. This will make it impossible for you do to several missions, but you can still finish the game.

Don't worry about it. Don't follow walkthroughs. Make your own path, deal with whatever consequences you incur. That's how you play Fallout. There is no "correct" path. Every playthough can be different.

That's a very good idea. I'll play as much as I can without walkthroughs. Seems there are multiple ways to solve the same issue. I wish they made more RPGs like this. :)

There are only three quests that you must complete to finish the game. The water chip is the first one. You find out about the other two after you find the water chip. (What, you didn't think it would be that easy, did you?)
There are dozens of other quests in the game that you can do or ignore at your pleasure. There are three things that the quests provide:
1. The experience points and loot the quests reward you with make your character more powerful, and therefore, more fun to play.
2. Some of the quests (and / or talking to folks) give you clues about how to solve the three main quests.
3. Your actions in many of the quests will determine what sort of cut scenes you see after you complete the game. Who gets a happy ending, who sucks it.
3. The quests give you something to do with your time (and let you see the world in action).
You can kill everyone you meet, loot their bodies, and get XP for their deaths. But overall, I think you get a bit more experience from helping people than killing everything that moves.
Towards the end of the game, you should be swimming in loot, so there's no real need to grind the entire population of the wastes under your boot to collect a few bullets and a handful of bottle caps.
What I usually do is wait until after I've fully explored an area before I read the walkthrough. I'm just checking to see if I missed anything important / interesting / amusing / entertaining. I'm usually able to figure out 90% of what's going on my own, but it's sometimes nice to go back and pick up the cool loot hidden in some container you forgot to check.
There's only one or two places where the game throws such a curve that you won't figure it out without the walkthrough.

Good tips. The hardest part is getting around. I guess my memory is pretty bad and it's hard to remember where one place is or not. Are there maps (links please) out there that don't give out spoilers, just basic locations like a city bus map would have - i.e. store/shop names, etc?
Thank you. :)

Lots of good advice in this thread, thanks for sharing.
escaped I'm not saying you smoke, but I know I used to enjoy the ganj a bit, and since I quit I've found I can remember locations much better these days ;)

Haha . I run my own business. I play Fallout during breaks, and travel, so it's hard to remember everything I'm doing in the game. Haven't hit the 'smoke' for over 2 decades. :)
I just wish there was a more detailed map system in game. Perhaps a mod was made for this?

Ah yes, that'll do it. I hope your business goes well! Ginko biloba is your friend :D

I've never seen a map that didn't have at least some spoilers on it. It's not as many spoilers as full walkthrough, but there are still spoilers. The map will show the layout of all the buildings and the locations of all the NPCs & Shops. But they usually tell you why an NPC is important or give away the locations of "Easter Egg" type loot. "There's $100 in unattended in the back bedroom" or "ask this random guy about poo for 100 xp and 20 round of ammo"; stuff like that.

Yah, exactly. That's why I'm trying to avoid those kinds of sites. I'll just start taking notes. :)