What I have generally found is that if you want lightweight, then you have to spend some cash. Strangely enough, if you want small, you have to spend more too...
Anyway, I have heard nothing but glowing reviews about the T61, so you should be ok with it. What all have you been able to configure for that $1000 at Lenovo's site?
Because I was looking at it, and you can get better specs on the Apple Education store on the MacBook. The T61 is a little bit lighter, but they are the same thickness, the MacBook has a killer screen (IMO), and is quite a bit more durable than it looks.