I've been playing NotR on Windows Server 2008 (for most purposes identical to Vista). After a few problems I got it running, by following some of the general Vista tips (specifically: installing the game outside of /program files/ and applying the PlayerKit mod which makes it possible to start the game without DirectMusic).
So it's playable, but I'm still having some very annoying problems, which strike either right after starting the game, or maybe every 10 minutes or so of gameplay (on average). One of these happens:
1) Extreme slow down of the entire game, including the game menu and save/reload screens. Only restarting the game fixes it.
2) The textures for the player/npcs/monsters vanish. So basically, everyone becomes invisible, you only see their swords floating in the air.
3) The textures for the environment vanishes; the ground, water, buildings...
2 and 3 can sometimes be fixed by reloading a game, but usually the newly loaded game will be bugged as well, so you're better off simply restarting the game.
So, any ideas on how to solve these?
I've tried the following already but they made no difference, if anything they made the situation worse:
gothic2_vdfs-patch
the IronKeep patch
the Sumpfis texture pack
running the game in various Compatibility Modes
running the game as admin
I also tried the gothic2_fix-2.6.0.0-rev1 (but it turned the game into german, which is a problem for me).

Try playing it on XP/Vista/7. Windows Server 2008 is not officially supported...

The server OS:es never are, but I've never experienced any major problems with it. In fact, the only game (old or new) that even required any extra tweaks was VTM:Bloodlines, which played just fine after the changing the installer to accept any platform.
My point: I suspect these issues are not uncommon problems on Vista.

Well, have you tried completely uninstalling the game and reinstalling it without any patches/mods?

Yes, but trying the game without any mods at all gave me this problem:
DirectMusic error
His solution didn't work for me though, however this one did:
Gothic 2 + Addon unter Vista
So that's the bare minimum for even getting the game to start.

nVidia or ATi video card? What driver version?

I'm on vista and I'm having some Vanishing texture problems as well. The environment turns pink and i see floating objects. inside house and caves are fine but the world outside is all bugged.

Yep, that's what happens to me too.
My video card is a nVidia (9800GT), with driver version 195.62

Same problem here. I have a nVidia card too, a GeForce 9500M GS, with driver version 195.62 as well.
EDIT: I forgot to mention that I use Windows Vista.

I'm on Vista 64 on an 8800 GTX. Previously, I had Gothic 2 installed and it all ran fine from the very start to the very end. Well, my hard drive died a couple months ago, and so I got a new one and reloaded everything back on. A few nights ago I redownload and reinstall this, and after no more than 5 minutes, NPCs and the ground disappears just like you guys are getting too. I'm assuming getting the latest video drivers screwed something up somewhere? Wish I knew what my previous driver version was. I tried running at both 16 and 32 bit resolutions but it didn't make any difference.
Either way, hope someone finds a solid solution. I can't be bothered to play with old drivers all day.
Also - just checked, same driver version as you guys too. 195.62. Pretty obvious what our culprit is then. All I can suggest is if you're willing, to get older drivers. How much older I can't say, but if someone experiments and finds a compatible driver version, please do post the version.
EDIT: Just checked the release notes of the latest driver release, 196.21. In the "Known Issues" list, it says "Gothic1/Gothic 2 - there is corruption and the game crashes." At least they know about it, who knows how long it'll take to fix. Older drivers is the only way you'll get this fixed for now.

Getting the same issue, got nVidia 9800GT video card, most likely it's the same drivers issue. Has anyone tried playing it with any newer drivers?

Nvidia has recently added Gothic to the "known issues" of their driver release notes, but they have yet to actually fix it. :(

so annoying. Same problem here, WINDOWS VISTA and textures vanish. Game is unplayable...

Not really helpful, but I built a new PC and rolled with an ATI card. Game works fine. Nvidia really needs to patch this bug for their users already.