Also, if I'm not mistaken, Office 2K uses heavily MSIE infrastructure, and MSIE still cannot be even installed on wine (without windows), so I suspect it's a ton of work to do.
This is an excellent and important point. Office depends on IE, but with Office XP, you can no longer legitimately install IE on Linux (the license for IE requires a valid MS license). Hence, Wine/Linux would be required to provide a full IE replacement in order to get Office XP to run...
You have the same problem with DirectX games (although Transgaming has more or less solved this one), and with Windows Media Player.
Jer