There are alot of things that could have caused that crashing, too many in fact to even list without trying some basic troubleshooting. Be glad that you did finally get it working and improved your render times.
Oh, by the way, if you are rendering animations and if your old pc is still operational and in your possession you may want to consider setting up a 2 node render farm. Even if your old pc was more than twice as slow rendering it can still render every 3rd or 4th frame in an animation resulting in a 25% - 33% (not counting for overhead) speed up.
Oh, that sounds interesting to have 2 computers working. But unfortunately the old pc is no longer mine.
But a question to you: Concerning the problem I described above, what to do if something like “not enough resources” comes from Blender (although blender was the only active program, 30 GB HD space free, and 1GB DDR400 RAM.
I’m assuming Windows XP here, if that’s not the case just ignore everything I say.
The only things I can think of that might cause that would be stuff that you don’t know is there running in the background (a ctrl-alt-delete to bring up task manager and check processes to see what all is running, look to see what is eating up all the cpu time and memory). The other thing that might be happening is a memory leak, this will also show up in task manager with one program having an absurd amound of memory listed. Blender might be the culpret itself and if it is you may want to try a different version or a different build (like the optimzed build in the News and Chat Forum). Also if it is blender and it happens during rendering animations you may have to render in smaller chunks. And finally if blender is doing it and you are using new features from a CVS build (like fluid simulation or soft body collisions) there is little you can do besides submitting a bug report.
I’ve never really used blender to intensively, but I also have never seen that error and I have just as much RAM and about 20 times the disk space of yoru rig.