What is killing my speed?

Hey guys -

Right now, I have a desktop running Windows XP hardwired to my router, an Apple Airport Extreme. I also have a MacBook with OS X and an Airport Express to extend my network's range.

I just tested my desktop's speeds, getting 15,359 kb/s down and 1313 kb/s up (Comcast). The laptop, however, is getting only 4991 kb/s down and 891 kb/s up. I have full signal strength. I'm currently broadcasting on channel 11.

I have WPA encryption enabled. I've read that can make a difference, but isn't that on older hardware only?

Could it be a bad card inside the MacBook?

I tested again, this time I wired the MacBook to the router.

I was getting 12,148 down 1,321 up on the Windows desktop.

Wired to the router, I'm getting 4,355 down, 1073 up on the MacBook. This must mean its a setting on the laptop, right?

Any tips would be appreciated and if you have any questions that will help you to help me feel free to ask.

What do you get when you bypass the router and plug the Macbook or the PC directly into the Modem?

Since it does it even Wired to the router that rules out any Airport issues including WPA as Wired does not use Encryption nor Airport. That is a LARGE speed drop there. Not really sure what is going on. Try Baggss suggestion and report back. That really makes no sense especially wired like that.

I take my iBook to a friends and even with Wifi 2 rooms away from his router I get with Comcast Cable 15,000+kb/s like you are getting on your PC and this is WiFi and a distance away.