If you are budget minded, a pentium m that you'll find in any number of given Dells on ebay coming back from corporate leases works just fine. You'll pay about $200.
Here's a link of just one, as an example:
http://cgi.ebay.com/1-DELL-LATITUDE-... em2307986d2e
or a low end core duo:
http://cgi.ebay.com/DELL-LATITUDE-LA... em45f340a008
Watch and only bid on the lower-priced ones. I came away with a 1.6 for $180 a couple months ago.
Edit: On another note, I just picked something with a bit more horsepower (a ridiculous amount for what you want) for a reasonable price after $250 off:
http://www.officedepot.com/a/product...41-Widescreen/