Kids Cancer Corner,
It appears you volunteered (or got volunteered), for a huge, somewhat technical task, that you have little or no experience in. You're going to receive videos delivered different ways, in several formats. WoW!!!!
I understand that the only equipment you're working with are a Mac and a PC. But we have to keep things kinda focused on issues specific to iMovie.-:)
As I mentioned earlier If contributors are able to create a video file for email, they're already familiar with some type of video editing application. Most of these applications/programs allow you to save the file at higher quality. I only mentioned "Movie Maker" because it's usually on all PCs.
Windows XP (SP2) supports "Movie Maker 2". Windows ME supports "Movie Maker 1" (I believe in MM1 the highest quality output would be, Video for broadband).
Re: Second Choice
Considering the limited options available, if you cannot find a video site that allows you to upload video without adding additonal compression, then I guess Google Video (mp4)is as good as it's going to get.
I suggest you familiarize yourself with Movie Maker and iMovie first. You need to have a grasp of basic principles/concepts. Read the help section of each program, and do the tutorials.
While you're waiting for the other videos practice on Daniel's mp4 video. Download it, convert it (using Mpeg Streamclip) to DV format and import it into iMovie.
Here's a great resource site for Movie Maker. The menu has a section for "saving movies"
http://www.papajohn.org/
Here's an excellent book you should read. Contains a lot of iMovie info. Should be able to find it (somewhere) dirt cheap ($10 - $20)
iMovie HD & iDVD 5 (Missing Manual)
by David Pogue
When you need additional help, you can create a new topic and post specific questions (or search the iMovie forum) regarding problems you may encounter with different formats. Don't worry someone will assist you, but this thread is rather long and will become confusing.
Good Luck