Sycamore,
My mother has an iBook G3/700 with 640MB RAM and OS 10.3 (she will have 10.4 very soon however), along with Office 2004.
It's quite a servicable system, and much better than the Dell desktop she has.
Failing that, I'd go for an IBM Thinkpad R50 or R51 on special from PC Connection. These machines come with XP Pro, and are the toughest laptops next to my Powerbook G4 12"

.
Mitch