If the above don't work and you've got the latest RealPlayer, then either the file is corrupt, or (much more likely) it's mislabeled.
You get a surprising number of screwed-up files from Windows users that have the wrong extension just so they open in the preferred program. For example, most Ogg Media (.ogm) files I've seen have an improper .avi extension. Likewise, I've seen .avi files mislabled .wmv or vice versa.
In this case, try giving it an .avi extension and see if VLC can do anything with it.
Worst case, it's one of those files with a totally inappropriate combination of codecs--something like an AVI container with Real video and WMA audio. If that's the case, you're probably out of luck--even Windows users often have trouble playing them. I have no idea why people produce some of these bizzare files when there's several perfectly good free and readily accessable codecs and container formats available, but they do happen on occasion.