Problems installing apps in W7

[#1]

Finally got round to installing W7. Can't install Kaspersky - apparantly there is a corrupt file (it is the latest version).
Neither can I download FF3.5 - that is supposed to be corrupt too.
Both were activated 'Run as Administrator'. Any suggestions please?
BTW it coped OK with Avast.

[#2]

Got my beloved Firefox installed so now I just have to try again with Kaspersky but will have to uninstall Avast first.