virtualbox.org

I switched from XP 32-bit to Vista Home Premium 64-bit. Then I used PC Mover to move program settings, including VB, but I did not know that there are separate VB versions. Now I can neither install 64-bit VB or uninstall the 32-bit one. Always getting the message "this application only runs on 32-bit systems".

Anyone can help?

Then you'd have to go into the registry and manually remove the vbox entries, risky business but with a 32/64bit mix probably the only way, just until the 64bit version no longer detects the 32 one.

Nope! Use this tool to remove VB from Add/Remove Programs and then you can install the new VB:

http://support.microsoft.com/kb/290301

Note this won't actually uninstall the old one but the new installer should overwrite all the old files.

Maybe yes, but in this case you need to be extra carefull with a mix of 32/64bit, I'd go the registry way which give you more control over whats being removed.