AT&T U-verse → markedly different speed test results b/w macs

I have a MacBook Pro from 2008 (first unibody) and a new macbook air (this year). I was noticing slow internet speeds on my macbook pro in my office, sometimes less than 1 mbps. If I put my macbook air right next to it , I'll get 6-7 mbps.

Does anyone know why I would be getting such significantly different speed test results between the two computers?

thanks.