Yes.  It uses a desktop P4 on a 400 MHz bus.  However, I'd be very careful about overheating - the system has enough trouble coping with the CPU as-shipped - if you put a faster CPU in, you may push it over the edge.

I agree with the poster above. It's probably possible but you should be careful.

Also, if it's performance you are worried about, why not wait a year and buy a new laptop? Dell offers some really good deals on the Internet from time to time. I think I saw a pretty good 9100 sold for about $1100 (1200 maybe?) the other day!