I have to use Office 2007 at work and don't like it much, but it's usable if you persevere - at home I use Office 2003 under XP, it's also OK under Vista / Windows 7. Office 2000 isn't supported at all any more, and is increasingly unstable under all versions of Windows, so I really can't recommend relying on it.
If you're going to be working on non-Windows PCs e.g. Linux your best bet is definitely Open Office, since it supports pretty much every operating system around. The learning curve can be steep since it sometimes LOOKS like it will behave the same way as Word but doesn't, but for most routine writing purposes it's fine.
