Avoid Centrino? I recommend you avoid Intel.
Built-in WiFi in a notebook's ad copy can mean a number of things. It can be incorporated into the processor, a la Centrino, incorporated onto the mainboard (which I think Fujitsu does in its P series notebooks) or it could mean that there is an internal miniPCI card present in the notebook. My Dell has a miniPCI slot free and I got a miniPCI 802.11b card on eBay for $50 USD. I did have a PCMCIA card but I got sick of forgetting to bring it with me.
I see IBM is pushing WiFi big time in their ThinkPad ads. I wonder what type of architecture they are using. Maybe
PreferBulkhead would know?