I used several times my old laptop for live recording (up to 16 simultaneous tracks), without any problem.
It was a Intel Core 2 duo P8600 2,4 GHz, 4 Go ram, Vista 32, bought in 2008, and the version of Sonar was 8.53 at this time, i think.
I think that recording doesn't need a very powerful PC (if there is not a lot of audio effects on the tracks with input monitoring, etc).
 

Rule of thumb is a low spec laptop with a good soundcard is better than the other way around, and if you don't mind higher latencies you can do quite well.

Thanks guys, I'm encouraged to move forward. Using a Fast Track Ultra sound card.