Well, I took a look at MortPlayer. I have to say that the stock skin is Fugly. Fortunately, it seems that their user base has added a handful of additional skins that aren't too bad. Overall, I'd prefer not to have to install a bunch of different media players on my system and since there's no way to pull Windows Media Player, I'd prefer to work with it.
I will try out MortPlayer, though, and let folks know if it'll still play music while TomTom 5 is running.
Also, I found the Microsoft link to PPC Media Player Skins:
PPC Skins
They kind of suck though.