If anyone else is still having this problem, uninstall your codecs and install CCCP

I tried some codec packs and all that did was trash my setup to where I couldn't play any movies at all. And since my computer is set up more for home theater than just games I felt like further experimentation with codecs just wasn't worth it for one game.

Does using the VP6 codec help the quality of these movies? They don't look that good on my computer (Windows 7 Home / GTX 460) and I'd rather use the original videos.

These videos work for me without installing an extra codec, though. There are another set that are much larger, but higher quality, that I would like to get to work, but I cannot get those to play through Thief at all.

So, does anyone know if installing the VP6 or CCCP codecs should improve my playback?

quality wise, no.

Fixed it, for me at least. I installed the K-Lite codec pack, with the larger re-encoded vids and that seemed to work. Also installed a beta version of ALchemy (see different thread) to enable EAX and that gave me EAX and sound in the videos too.

All is working wonderfully for me, and right now the Bonehoard beckons!