A/V Receiver Question

Hey guys hows it going, im pretty new to the whole Home Theater thing and I have a couple basic questions as I am finaly on my quest to building a home theater.

My main question is with the Audio / Video receiver. The componets of my system are going to be, naturally a tv, a xbox360, the hd cable box, and a blu ray dvd player. Now in a perfect world, do I want each componet running to a HDMI slot on the AV Receiver while that then runs to the tv? Then you would have to switch between the xbox, the dvd, and cable??

My other question has to do with the upconversation of a AV Receiver. I notice alot of the receivers only upconvert to 1080i (The Tv is capable of 1080p). What happens when a 1080p singal is running threw the receiver, im assuming and hoping that if a 1080p signal goes in, it comes out 1080p also, does the fact that the receiver cant upconvert to 1080p means it will pull it down to the highest it can upconvert (Which assuming in my case it is 1080i)? (I realize this may be a stupid question but I would like to double check anyway).

The componets of the system: The Samsung 46" LN-S4696D LCD . Xbox 360 Elite (HDMI Port), Blu-Ray Dvd player (Undecided I just know I do not want the Playstation 3 as my player), The cable box, I also havnt decided on any speakers or a specific av receiver yet but have decided to go this route (If anybody has any honorable mentions by all means I am interested).

I will say thanks in advance and hope everyones summer is going well, cheers~

But then you can't hear the voice of the cable box from the additional speakers you buy.