OK, I did a search & found alot of threads about upconverting, but...

Can someone explain (in NOOB-friendly language) what exactly it is/does, and what the benefits are from it? Does it turn a 480p signal into 720p? Do you lose quality?

Basically, think of a low-resolution picture, for example a picture you wanted to put on your computer desktop.

Say your monitor supports 1024x768 but you have this awesome Batman wallpaper that's 640x480. If you keep at its original size, it's too small, but crisp. If you stretch it out, it'll become blurry.

Upconversion lets you stretch out the image but will clean it up so it's no blurry.

It won't like as good as if it were truly a 1024x668 well done version of that wallpaper, but it will look very crisp compared to original when stretched.

I don't think I've heard anyone saw they lose quality or detail in upconversion, and in general I've never heard it ever be worse than original 480p if you have a good upconverting dvd player or tv.

OK, sounds good so far...

Are SD DVD's in 480i, and upconverting will put them into '480p'?

"progressive" DVD players will put them into 480p

Upconverting will send the signal out at 720p, 1080i or sometimes 1080p.

Also, be careful with regards to receivers that say they upconvert. My Denon says it upconverts, but in reality, all it does is changes an analog signal to digital so I can just use one HDMI cable from the receiver to the TV.

OK, so I'm using the Xbox 360 & HD-DVD add-on, do either upconvert?

Only if you use the VGA connector - otherwise standard def DVD's will only play at 480p.

HD-DVD's will play at the output you have selected in the dashboard.