Step 1 Read
The Perfect Store: Inside eBay Adam Cohen
Step 2. Create software for business to multilist easily ... you know like ebay has.....
and why you are at it make software to load for the public as well you know like ebay has....
Step 3. Give that software away to small business
Step 4. Go through the online forum that TM runs and make a list of the thousands of gripes that people have about TM then take the top 20 and do the opposite
Step 5 Make a proper forum for customers and sellers to interact on
Step 6 When you decide on a name Please check that it can be spelt has one meaning or it doesnt mean anything at all and that you buy all the domains. Just incase one is a porn site! "Really? that would never happen!"
Side thought Get 100 geeks to produce software as a open source project.
I am sure you can add to the list and of course you will still need a bit to get it going
Of course you may be able to get Pierre Omidyar to help out..............