I believe I stand corrected! Buffalo only supports this to work with one computer, however there are work arounds that should get it to work with more than 1 though not many as it will slow down the NAS (which is why its only supported for one at a time), but here it is... It is also recommended that you set each computer up to different shares to minimize any confusion in either software....
TO SETUP A TIME MACHINE SPARSEBUNDLE:
1. Open up the Terminal (Open up Finder->Applications->Utilities)
2. In the command line type in the following:
hdiutil create -fs HFS+J -size [Size_in_GB]g -volname "Backup of[computer_name]"[computer_name]_[Ethernet_MAC_address].sparsebundle
3. Press enter after that long command and you should have a sparsebundle file created on your desktop or User folder
4. Move the sparsebundle file to a folder on the NAS (say TimeMachine for example)
Q: When specifying the sparsebundle size does that mean the sparsebundle itself will be that large?
A: No. Specifying the sparsebundle size in the commandline tells Time Machine when it will start deleting older setups inorder to make room for newer.
Again, this is not a supported work around but is known to work!
*KUDOS to Dustrega for this info*