I just bought HDMI and component wall plates for my install. Now, do you need a box to put these in or do the plates just install onto the wall? If it requires a box, which one do I use?

You would want to use a box. The open boxes from Carlon work well.

http://www.hometech.com/techwire/cn-sc100a.gif

Carlon Box (http://www.hometech.com/techwire/wallboxlv.html#CN-SC100A)

I use these wallboxes for retrofit installations:

http://www.hometech.com/techwire/cn-sc100rr.jpg

Thanks!!