It is interesting how much Media Center relies on Windows services and other programs. (Compared to other solutions like XBMC)
I couldn't find the screensaver and looked around the forum and finally figured out there is none, just ways to work with the Windows built in Screensaver.
(Which works fine for me)
The way I figure it, You import the iso as data, then change it to a Movie Subtype, then get info.
To play you set MC to launch Virtual Clone Drive, and mount the iso you clicked. Windows itself then sees the new drive letter and Windows Autoplay (if configured right) will try to play it with Media Center, which you already have open. It works for me, but a few seconds delay while the magic happens in the background. Much faster with just folders of the ISOs, but you do lose it being the ISO...
For playback, hesitation and jerkiness can be Video (hardware/software) or Network. Is this file local? Can your machine play it with another program once it is mounted? (ie Media Player Classic, part of the K-Lite Pack or Cyberlinks PowerDVD).
If it can then you need to look at how MC is set up, if it can't, MC isn't the problem.
my 2 cents worth..
Don