DVD ripping is not in itself a particularly cycle intensive process - however the Encoding is another matter.
If you intend to convert the DVD's into something more compact such as DIVX / H.264 then you can end up with pretty much the same quality for 6-7x less storage.
Any current dual-core (or better) processor is more than up to the task.
As stated above - the RAM is the main issue so go for 4gb+ (you must have 64bit OS to benefit from more than 3.2GB)
Tom's Hardware: Hardware News, Tests and Reviews is a goldmine of accessible (sometimes rather geeky) information.
Also -
Doom9.net - The Definitive DVD Backup Resource is pretty much a one-stop-shop for all things media related.