My PC isn't "good" enough to run this game on the highest possible settings, so i turn it down to an appropriate level, then a couple of hours into the game it automatically turns to the highest settings and crashes my PC, can anyone help me with this problem?

Try deleting the file Running.ini from C:\Documents and Settings\[Your Username]\Application Data\ to prevent settings from reverting back to default. Let me know if it works or if it doesn't.

I actually tried reinstalling it and it -seems- to be working now. If I encounter the problem again I'll try what you suggested then post it here or drop you a PM, thanks for the help.