I've never used Vista MCE, but I know with XP MCE it was a pretty easy process to trial MP.
Just install and configure. When it is set up and running, it disables MCE so there's no conflicts.
If you don't like it, then just close down MP and the TV Server and MCE will run again.
I'm sure someone will correct me if things have changed since I last tried this.
BazzUK, I have tried XP MCE for 2 years. In that time I have changed my TV tuner from PVR500MCE (Dual) to 2x floppydtv DVB-T. MCE works in beginning but starts stuttering after several months. I changed to MP because I hoped it was more stable. I must say: IT IS MORE STABLE. Instead of crashing every 3 days now it crashes once a month (mostly because I have done something wrong or installed a beta plugin or something)