Christo, I had more or less the same problems when I had 2 GB Ram. Mount & Blade in general seems to have some kind of weak engine or whatever, never saw a game that crashes so much^^
But when I upgraded from 2 to 4 GB it became less worse. Now I only get crashes from time to time, usually when I alt+tab too often
Some mods for warband always crash after 5 seconds when you have less than 4 GB
I hope it works for you to put some into it (if you have trouble to find out what fits into your pc I bet someone here is able to help you^^ )