You cannot convert the for-pay downloads.
The best you can do is hook the computer up to a DVD recorder or VCR and capture it. But
iTunes/Apple uses a real bastardized version of H.264 compression, so you tend to have choppy video with artifacts. The
iTunes files only look good on newer Core 2 Duo systems, and even then only the Mac OS X version of iTunes playing it.
This is something I'd do with my laptop.
Regardless of what you try, it's a low-res video made for an iPod screen, it's hardly worth watching on a television unless you're just really that desperate to see it. Literally "for die-hard fans only" land.