New computer and new OS?
On the old one any updating should be done with uninstalling through GameStop (Impulse).
On the new one? Opt for clean install via the link in RedneckDude's link.
Many of the skins have been updated for Windows 7. So, pick and choose. Any Masterskins purchased through Maxstyles... save receipt emails and
transfer to the new system... same as any receipts from Stardock (although they are part of Stardock's records, having proof never hurt).
Finally, If you're concerned about Registry keys being left over, after uninstalling, run ccleaner's registry tool, but make a backup of the registry and a restore point before uninstalling, and cleaning the registry.
