Vegas 7 Rendering Problem (process freezes)

Okay I've a 1.5h video with lots of source materials in different formats (mpeg, mov, avi), different transitions (but mostly fades), several effects (most of them are color corrections) and about 45 mp3's.
It is completly in half-hd (720p) and has 5.1 sound.
I did the whole Project in my free time so it took me about 3/4 of a year.
Now when im trying to render the process freezes and only the estimated time increases.
I tried rendering on three different computers:
- vista x64, core2quad, 8gig ram
- the same pc with xp x86, which results in 3.3 gig ram
- xp x86, amd athlon 2800+, 1.5gig ram

I tried rendering in many different formats including

- mpeg 2
- mpeg 4
- avi (divx, xvid, cinepack-whatever)
- and even wmv

every format stoped rendering at about 35 frames.

Now, I totally ran out of ideas and the movie should be rendered by friday evening.

greetings, Jan