Sure. It's not recommended to have 2 active anti-virus programs. That's even more the case if one of them is outdated or gives problems.
Kaspersky doesn't come with Windows. It has been added by somebody (maybe you, maybe the maker of the computer, but Microsoft doesn't do it). But that's not really important any more.
I recently purchased and installed Avast 7. Is it safe for me to uninstall the Kaspersky that came w/ my windows vista? (I've had computer problems related to the outdated Kaspersky)