Does the PCCard have an antenna that you can place anywhere you want, or is it just attached right to the card?
I doubt you'd see any differences in performance between the two card types; 32-bit PCCard is basically a PCI connection, tiny bit of latency added because of the bridge. If you get an adapter card, that leaves you the option to use the PCCard with a laptop if you needed to. If you just get a PCI wireless card, then you've still got the PCCard wireless if you wanted to use it on a laptop, and you wouldn't have to disconnect your desktop.
Cheapest adapter is 25 bucks shipped on newegg. Cheapest PCI wireless is 23 shipped, and a 10 dollar rebate.
