I typically try to put VS 2003 on the Dev Server. It’s not required – I just makes like easier. In BizTalk 2006, you can do everything in the Admin tool. In 2004, it is not the case. It is required on the workstations.
Office, or at least Excel, it required on the server and workstations only if you are using and installing BAM.
On the workstations, I think you just need the Developer Tools. Might want to make sure you get the Documentation and SDK as well. If using BAM – you might need one of the BAM pieces. I not sure on that.
Hope this helps.