Good Laptop for Knoppix-STD

I'm hoping to put Knoppix Security Tools Distribution on a Laptop.
I have a limited budget and was wondering if anyone had suggestions for what type of power i would need in terms of CPU, RAM, etc. Or any good brands or models they might suggest. I was thinking I might buy an old IBM thinkpad. I need suggestions and any would be good.

I've had great luck buying used desktops and laptops over at the Dell auction (www.dellauction.com). Dell auctions off machines that they've brought back from lease and have refurbished.