I'll PM you the best source to get RAW's from. If you want to do a good job, you'll find that you need to recompile your RAW episodes before using them. I tend to find that wmv format works best for video editting, whereas avi and mp4 are both a chore for the software to load properly for editting (higher wait times and bad preview quality). I also find that it works best to compile the RAW wmv's with Windows Movie Maker, and use those recompiled videos to make your AMV with. I've personally had experiences of Vegas acting weird when I tried to use wmv's that it compiled, so I wound up using WMM in the end for that task. WMM can only do HD videos if you have the Vista version or better.
You'll find that some newer HD RAW episodes you download wont work at all with most programs. For those, you'll want to download "RAD Video Tools" by Bink and Smacker. With that program you can recompile pretty much any video file into a standard xvid avi that can be worked with. In a worst case scenario I find myself recompiling a RAW episode 3 times (RAD to read in Vegas, then Vegas to read in WMM, then WMM for the final encode) in order to get it into a format that I like to use. As you know, I use Vegas to make the AMV once I have all my episodes encoded the way I like and ready to go.
EDIT: RAD Video Tools is a free program, so there's no need to worry about that. I've heard that Adobe Premiere is a good program for video editting as well, but I personally have no experience with it.