Never heard of one. But, i could guess that perhaps it's actually a .rm video file? Usually .rm is RealMedia and can be viewed in RealPlayer. There's no official way to import a RealMedia file into anything other than RealPlayer. I have heard that there are a few unsanctioned hacks out there though.
I'd suggest trying to open it in various players/viewers, questioning whomever you got the file from, & failing both of those, get a large cup of coffee and google it.
RE: Real video editing, Not sure if it will work in Vegas, probably a way to use avisynth, but there is an open source filter available -> check the news & link to the thread at doom9.org. Don't know if I'd quite call it unsanctioned - developer of the real video codec is prominant in the thread...