Back to square one: new iTunes and QuickTime CRASH, CRASH, CRASH

Question

I've been struggling with iTunes and QuickTime ever since the upgrade to 6.0.4. Everything worked just fine until then, and has worked fine since I got my iPod last June.
A couple of days after the upgrade to 6.0.4 iTune started crashing, with the error message: iTunes has encountered a problem and needs to close. We are sorry for the inconvenience.
Please note this is only about using iTunes to play music on my computer (my iPod seems to be working fine.)
I've removed iTunes and QuickTime, reinstalled them, and this works for a couple of days, then iTunes starts crashing again (this has now happened twice.)
Strangely, this time, tunes in Party Shuffle at start up (from the last normal exit of iTunes) play just fine, but when I try to play something out of Library or swtich to a different genre or playlist in Party Shuffle, the programme crashes: iTunes has encountered a problem and needs to close. We are sorry for the inconvenience.
I've tried opening QuickTime alone, and it fails to open (no error message) it gets as far as the player, then there's a windows "thunk" and QuickTime closes.
So now I will uninstall, reinstall (starting with QuickTime, which seems to be the real culprit here) and maybe it will work for a couple of days. Computers are supposed to save time, not take up time in this way.
I don't seen any sign or word of a new version of QuickTime with a fix to this problem (many seem to be having it). How long do I have to go on this way. Perhaps the best is just to use another Windows Media Player or Nero ShowTime ... these seem to function without any sort of problem.

Answer 1

Thank you Katrina and MossMan,
I do keep my computer under pretty tight wraps: Outpost firewall, AVG anti-virus, MS Anti-spyware. Ran the Ewido scan as suggested, Ewido did find quite a few cookies it considered of medium threat spyware ... removed these, and this did not resolve the problem with iTunes/QuickTime. Anyway, I'm not sure that cookies can cause programmes to crash?
I still think that it's unlikely that the problem with iTunes and QuickTime starting right after the upgrade to iTunes 6.0.4 and its QuickTime counterpart, is just a coincidence.
And if QuickTime is particularly vulnerable to some malware that none of the security programmes on my machine can find, and malware that has no effect on any other programmes, including other media players, then maybe this vulnerablity should also be something Apple should try to address.
Walter