OT Place to buy a 300-400 Mhz

I am looking to put together a computer as gift for a friend. She is not
a gamer and the most intensive task that I imagine her doing is burning
cd's. As I would not have physical or network access to the box once it
is given Linux is off limits for the time being. I know I suck, but it
would everything except the OS will be GNU. Give me a year and I will be
confident about giving a linux box as a gift.

I am thinking that an 300-400 Mhz box (or faster amd equivilant) with as
(256 ish) much ram as will fit would be good enough. Are my assumptions
correct for a win 98/2000 box? Also how much would such a box cost, and
where would be a good place to buy one?

I can do the OS install myself if needed...