I lucked into testing this last month at the office. We took a clean machine and installed "XP". That is XP from a "XP" CD and not a XP SP1 or later CD.
Not only did the wifi run at a 54Mbps speed limit but we could only connect to WEP or unprotected networks. After what looks like 200+ updates it now connects to the router at 150ish Mbps.
Keep in mind that all that is when we are 10 feet from the router and ideal conditions.
i am not able to connect at wireless n speed even though i have a wireless n adapter. i can force it but when i do my throughput drops dramatically, 20Mbps -> 1 Mbps. so i try, wpa2 security and can connect to router at 130 Mbps but throughput is 1Mbps when I throttle down connection to only connect at 54Mbps throughput is 20Mbps. i am running windows xp sp3 i heard that might be part of the problem. thanks in advance for the help...