what do you mean by 'got a problem here with QuickTime trying to access the content guide on start-up.'?
Sorry, that was a bit cryptic. By dfault when opening QuickTime it goes to the content guide. It goes online to get the information in the content guide. So if a firewall rule (say) is blocking QuickTime access to the internet, QuickTime can refuse to load when launched from the Startup/Desktop icons. But since QuickTime itself is fully functional, iTunes will often launch under those circumstances. That seemed to be fitting your symptoms.
But in those cases, often people can get QuickTime to launch if they open a local QuickTime-readible file on the PC. (Because QuickTime doesn't go to the content guide under those circumstances.)
We'd still better check on security software (given that your iTunes is currently launching).
What security software do you have installed on the PC? (Firewall, antivirus, antispyware?)