Can someone please tell me if the PCI 2.1 is the standard slot for desktop machines, and for how long it has been fitted to PCs? I wish to add a Belkin USB 2 card, which requires a PCI 2.1 slot, to my IBM Aptiva 2139 E57 (1998 vintage) but I am unsure if the PC's slots are in fact PCI 2.1. The computer's manual does not mention the type of slot and the IBM site doesn't cover these elderly models! Any help will be appreciated, as I have no wish to upset a PC that still gives good service. Thank you.