Sigh, I'd be playing it right now if I could find a mirror worth shit to download from.
Fileshack doesn't support download accelerators (which I need to be able to complete a download this size on my connection). The official link is either not loading or when it does only a fraction of pieces are actually downloadable. Coudnt find any good torrents that would sustain a decent speed for me either (yet).Unless you're referring to some of the tweaks the community made that were applied when filming that video, build 1935 is not a mod mate. Its a pre-release build.
edit
Finally found a good torrent. Going to take a while to download but I can wait. Its pretty awesome to finally get a chance to play all those locations I saw in the screenshots back in the day that didn't make it into the final build.

Can you link to the torrent so we can all enjoy a fast download?

This is the one I used:
http://btjunkie.org/torrent/STALKER-OBLIVION-LOST-build-1935-16-oct-2004/3952bb4e4bf5f0eb7d2a67428a5e937536c4b47a91aa
Essentially they're all the same since its bay tracker all in all.

Couldn't get the bay one, it was down.

Yeah I noticed, that's why I included mentioning the junkie one.
Back on topic.
I just watched the video, this looks rather amazing.
So if I get this straight this is considered a gold mine to the mod community?
Or is it difficult to alter this to your own needs?

Not at all. If you check the official thread there are already mods, tweaks and patches for it. I wouldn't be surprised if further down the line there will be integrations of the 1935 build levels with the retail build.
As it is now, these are purely for exploration purposes as there isn't really all that much to do. Its just geometry templates. It is amusing to see how much the game changed over the years though.
Also was watching this video:
http://www.youtube.com/watch?v=JbqQCzgBWbU
And as surprising as it may sound this version of garbage is much more fluid environmentally than what actually ended up being in the game. When I was in garbage I always got a feeling like as if they just made a random map size and filled it with templates they already had (don't get that vibe from this one though). Hmph, I wonder why they ended up remodelling it? I suppose it must be for the game progression purposes. This one is a bit more confusing than the streamlined final is.

This is so cool that they posted something like this. Now if I even beat the retail version (which may take forever), I'll check it out.

It's only a long game if you're no good at shooters.

I am good at FPS's, but this game is freakin' brutal (I'm playing on the hardest settings). Plus I have no idea what quest advances the story and what quest is simply a ridiculously awesome, but time consuming, side quest.

An easy way to determine if the quest is relevant to main story progression is weather its got expiration conditions (i.e. do this and this in 2 days or ur fakt roflmao). If it doesn't than it is (likely) a main story quest, if it does its a side quest. No main story quests have expiration conditions but some side quests don't either. This hint doesn't exactly "paint the picture" I know but it should point you in the right direction.
Oh and I'm pretty sure you're fine trying out the beta build. Its got no story or quests what so ever.

I say this game has an accurate simulation of how black holes are formed.
http://www.youtube.com/watch?v=Xc5rB-0ZBcI

By spinning aged eastern European cars out of control? :P

seriously the original S.T.A.L.K.E.R. retail release bored me to death.

Yeah its not really for everyone. Actually I see it as more of a diametrical opposite to the more conventional shooters such as CoD4 or say Unreal where gratification for progress is instant. Here you have to literally work for every single inch of land you traverse since even the environment itself is hostile (anomalies, radiation etc.). Personally I am big on the setting of the game which is likely the reason why I finished it 4 times already.