After experiencing several iTunes crashes I decided it was time to start fresh and reinstall iTunes.
Make sure you've completely uninstalled all the iTunes bits before re-installing. This Apple article details how to completely uninstall iTunes components from Win7
. Re-install and see how things go....
If you still have problems, your anti-virus may be stomping on the library file whenever iTunes tries to rewrite it. If you have a bunch of .temp files in the "iTunes" folder (or whatever folder holds the current "iTunes Library.itl" file) you can be fairly certain A-V software is at work. Set your A-V to exclude the "iTunes" folder and see how things go. (Even if you don't see a bunch of .temp files, try this anyway.)