I have "exactly" the same problem as iff_delta.
When i've clicked on a server to join, its starts to load, hits the splash screen and then just goes black and throws a wobbler, no error mesage or nothing.
It started happening the same way too.
At first mp was fine n' dandy, then it started the black screen thing.
To get it working again I had to do a complete re-install of COD2 even though sp was still working.
Now its happened again and i'm gonna have to re-install it (again)
Even though mp is messed up, sp works perfectly. I can run it @ 1024x768, Dx9, graphics settings maxd out with anistropic filtering and x2 AA and still get a decent framerate with no crashes or freezes, so no problems there.
The only changes I made to COD2 was install some sp mods:
wcp_realism, wcp_tracer and a blood mod. I've even tried removing all mp and sp mods, but the problem is still there, (perfect modded sp, but messed up mp).
Oh, the only other thing I changed was set "hunkmegs to 512mb" for both sp and mp, sp seems happy with it.
Plus, when I re-installed COD2 again it had saved the old "hunkmegs config" and mp worked, so its not changing the hunkmegs thats causing the problem.
So, maybe the problem is either a bug with COD2 (hopfully a patch will sort it) or the mods are causing or have caused the problem. the sp and mp mods I use are very popular, but this problem dosn't seem that popular, so maybe it not the mods... i dunno... I've never had a problem with COD or UO like this before.
If anyone else has this problem, post an let us know, it may very well be a bug within COD2.
My Specs:
Win XP sp2, 3.6ghz P4, Ati x8oo xt platinum, 1gb corsair twinx, abit IC7-MAX3 mobo, creative audigy 2.