Hi! Welcome to the forums!
I've read elsewhere that SP3 offers a brand new set of problems/issues for various users, particularly when it comes to networking hardware and software.
I myself am running XP SP3 (slipstreamed from SP2) and cannot get AC to work nicely with SP3. My fix, rather simple one, was to uninstall AC completely and use
Intel's wifi manager for my 4965 AGN card. Wifi works like a Swiss clock now, never any issue connecting or finding my AP's.
Only thing to keep in mind is to install the wifi drivers provided by Lenovo first and then only install Intel's wifi manager, otherwise you'll lose the Fn-F5 functionality.
Probably not the answer you sought, but at least you'll have a nicely configured wifi manager to get you by as an alternative to AC.
Hope this helps