Anonymous,
as a minimum, you need a development box with BizTalk and Visual Studio installed. You also need SQL Server somewhere (can also be on the same box).
After that, you can work remotely with Remote Desktop.
Or you can install the BizTalk client bits on a client developer machine and point to the remote BizTalk database. (At least, this was possible in BTS 2004 – I haven't checked in 2006).
John D.