Open Office v. 1.1.x runs pretty well on Linux with a 500mhz system. At work I used it successfully on a 933mhz Windblows system under NT, 2000, and briefly XP. And that's with all kinds of network & background junk that our agency makes everyone run. (I justify have this "non-standard" software on my box because I use the PDF export function.)
Yes, it probably takes a bit longer to boot than M$ Word. After all it has to fire up an alternate display system first.
I upgraded at both work & home, so I can't speak to a minimum system for OOo version 2.x.
