As per tMM's announcement here, and the "how to" guide here, this is the thread to post items which you are bidding on. This can be any item, music or non-music related (don't forget the fff policy though folks ). If you win the bid, a small percentage of the eBay fee will be added to tMP's funds. There are absolutely no increase in costs to the buyer or to the seller.
If you don't wish others to see what you're buying, (who knows, they may try and outbid you ) then you can, of course, send the link in a PM to yourself.
At the close of bidding, if you could quote your original post and state whether or not you were successul and won the bid, that'd be great.
Of course, if it is a "buy it now" item, you could state that when you post your link.