The "Wi-Fi" distinction is actually a certification by a vendor alliance whose purpose is to ensure 802.11b interoperability. When 802.11 (and then b) first came out, interoperability was a mess -- so, in those days, you just bought all Lucent WaveLAN (now branded Orinoco and sold to some company yet again) if you wanted it to really work. Vendors created the Wi-Fi group, standard, and certification to help vendors get together on this and to give customers some better confidence that arbitrary vendors' stuff would actually interoperate. So if it carries the "Wi-Fi" logo, that means it's supposed to interoperate with other "Wi-Fi" logo carrying equipment.
EXCEPT if there are extra proprietary "enhancements." Like the "802.11b turbo" from TI. Or enhanced security features from various vendors. You should be able to turn that stuff off and get all "Wi-Fi" equipment to interoperate at that baseline, however.
Do note that many vendors' PCI solutions are a PCI<->PCMCIA adapter card and their PCMCIA 802.11b card, and in general you need to get the adapter and the 802.11b card from the same vendor if you want to be sure it's going to work. (you can try mixing, some combinations work, some don't, but it's a ton of headache). I've never used the USB adapters but the argument made for them -- being able to get the antenna well above your PC case -- is a good one.