I had purchased a Samsung HD 841 DVD player that Up converts to 720p & 1081i through DVI... I ended up retuning the player because of the blacks lacking on the player. But there are up converting players out there. I did not really notice a huge difference but it did look cleaner.
There is also a Zenith player that up converts through component's also.
Lots of good talk about these players here:
http://www.avsforum.com/avs-vb/forum...?s=&forumid=18
-Dave