We have a download here (http://forum.outpost2.net/index.php/topic,5712.0.html
) that with a DOSBox/Win3.11 setup with Outpost already installed and ready to go. It makes playing it a lot easier as 64-Bit versions of windows dropped support for 16-bit applications. It also has all of the latest official patches (up to v1.5) that were ever released so if you're feeling nostalgic and want to remember the train wreck that it was, by all means.
As for OPU vs NTCS -- the problems with OPU's unreliable server have been resolved. The website's software has been updated and I think is still being configured -- need to check in with Hooman and Arklon on that. I personally prefer OPU because this is where my roots began in the fan community. I am a member of NTCS but OPU's activity, especially over the last 8 months, is much higher. But that's just my personal preference, I don't see one as better than the other. Me, Lev and Drakmar (NTCS's operator) have agreed that we should act as sister sites instead of competitors. I always say if you're joining OPU consider joining NTCS as well.
We still have our QuakeNet IRC channel if you wanted to drop in and say hi (you can use the Chat link above for an embedded web client or head over to quakenet.org and use their webchat, channel #Outpost2) we're usually around. Well, me, Lev, Dave, Brekkjern and a few others.
Here's hoping to see you join in the fun! Over on IRC they still actively host and play Outpost 2 multiplayer games. Sundays are typically the most active for that though Friday/Saturday during the mid-day to evenings you'll find plenty of people ready to play.
You mentioned Outpost and liking single player games. It's not finished yet but it's partially playable and I'm still working on it:http://forum.outpost2.net/index.php/board,106.0.html