If you're signed into google all your old apps will stay in the Market until you reboot the phone for the 1st time. This is the easiest way to re-download everything. After the 1st reboot, only purchased apps will continue too show.
If you've side loaded any apps (added them via means other than the market place) it won't show up in the market place anyways... Programs that "backup" your apps to the memory card will NOT retain the data to install them and have them show up in the Downloads area of the market - unless you've rooted your phone (and not all of them will do that then either)