I don't use or buy DRMed tracks, so I don't know
for sure if this is worth the effort.
However, I do remember a very similar issue (without the iPod stuff) that was solved a long while back by completely un/reinstalling both iTunes
and Quicktime. I've had to do this procedure once or twice for other Quicktime playback problems. I think occasionally, Apple does a less-than-perfect job of "upgrading" Quicktime, and a full removal and install from scratch is needed.
Since both iTunes and Quicktime install system and startup services, the best method is:
1. Uninstall both completely. No need to kill the iTunes database.
2. REBOOT. Don't skip because you are lazy.
3. Re-download newest version (only came out last week, so is quite new).
4. Install both from scratch. I like to install Quicktime
via this guide's instructions, to avoid evil.
So... I can't make any promises, but like I said, I have seen it cure my own ills before, and I'm pretty sure it helped with a previous iTunes DRM Video playback problem a while back. Might be worth the 30 minutes to try...