first, WMP doesn't have a dvd codec (el cheapos in redmond never bothered with it). WMP is rather piggy backing on another dvd software player, interactual in your case. VLC has an open source dvd codec build in (libdvdcss) that is using a brute force algorithm to ignore the region code.
RPC1 drives can play ANY region but are dependant on the installed player software to control which region is played. so if your interactual player (which is using the proprietary dvd codec) is set to region 1 you are not able to play any other region DVDs (that goes for WMP too), while VLC doesn't give a rat's.
RPC2 hardware, however, allows you to change the region a very generous FIVE times, after that your drive is permanently locked into the last changed region (hardware lock, even reformatting your hard drive or connecting the dvd drive to another pc will not unlock the drive).
libdvdcss is violating the copyright laws in many countries, hence no linux distro is shipped with this codec. using VLC to playback DVDs is illegal in many countries (e.g. the US of A or France, the origin of VLC)
