Best source to purchase newest version of MS Office?

What's the best place to purchase the newest version of MS Office software?

I am looking to upgrade from my Office 97 suite.

Also, which do you recommend, the regular Office suite or the Professional, or other version?

Also, what is the most recent version? I've seen both Office XP and Office 2003 various places on the web, but only Office 2003 on the Microsoft website.

Thanks,

General Tsao