Sounds like the wrong wireless encryption type
Or the wifi's driver. Vista is notorious for crappy hardware drivers.
Have you tried different protocol/security encryption as MsRaye suggested?
I'd first go into the "my computer" screen, change it to "clasic view" and nose thru the wireless and the security settings and make trusted sites lower security.
What sort of antivirus is it running, there may be a difference in the wired vs wireless settings there.
Then see if the wireless adapter settings have some sort of needed software/driver update
I uninstalled G-Data antivirus, turned off windows firewall, went to the wireless adapter properties and clicked on serch the internet for updates and it froze up. I'm ready to throw this laptop in the trash.
that seemns to be microsoft and apples answers..
But first, use a working ethernet connection to update the laptop and drivers for the wireless card.
Microsoft security essentials and firewall should be enough protection, don't load more than one antivirus program.
Do a microsoft aut update as well, search for updates there.