I'd recommend the K-Lite Codec pack
It's a collection of codecs for playing all sorts of things including DVDs (you'd have to select one of the MPEG2 players to play DVDs). The homepage is here. There are several variants to choose from, but if you just want DVD playback, I'd go for the Standard variant. Some of the other variants even add support for playing RealMedia files.

As for Media Player Classic, it's an open-source project, so it's only likely to contain a trojan if you downloaded it from somewhere dodgy. Some of the K-Lite codec packs contain MPC as a component.

EDIT: The K-Lite codec pack has it's own Wikipedia article.
( mistaspakkaman and the inedible shifting caterpillars, Sun 1 Mar 2009, 14:28, Reply)