[Windcatcher]

I bought Lycoris Desktop/LX (developer version) for $40. You can get the consumer version for $30 (if you want support), or you could download it for free.

OpenOffice.org: FREE
Mozilla: FREE
CodeWeavers Crossover Office: $50. buy it ONLY if you NEED MS Office or certain Windows apps.

It depends on what you want the computer for. From experience, Lycoris is good enough that my father could probably use it with only an hour's worth of handholding or so.

[Stillwillin]

Codeweavers also offers a module called Crossover Plugin.~$25.
CrossOver allows you to execute Windows web browser plug-ins in Linux.Highly recommended.