Wifi speed differences between OS X and XP

Hey guys,

I am currently running 3 systems on my home network.

1 Notebook. Apple Macbook (Core Duo) running 10.5.8
1 Netbook. Acer Aspire One D250 running XP
1 PC. Dell Dimension 3000 (PoS) running XP

The Macbook and Netbook are both connected via Wifi, while the PC is connected via network cable to my Macbook with Internet sharing on.

Out of curiosity I ran a speed test (speedtest.net) to see if there was any difference between what I was getting through Wifi, and through sharing.

Here are the results from my Macbook:



And here is the result from my PC:



I could understand losing some speed going from wifi to internet sharing, but I also get 8-9 mbps download results on my netbook.

Any reason why XP is getting a slower connection by such a large margin, regardless of wireless or shared? Turning off XP firewall has no effect.

Edit: Don't mind the time difference between this post and the macbook test time. I realized I clicked on a different test server after I had posted this and just did a quick retest. Test results are the same regardless.