I'm not too familiar with all the virus's out there, but I'm gonna guess a little more info may be needed. Such as are you sure the URL when logging in to FB is the proper FB URL and not something made to look like it or just ambiguous? Are you accessing the FB login page from something like a book mark that should be right, manually typing it in, or from a link somewhere? Is it taking you to a specific myspace page, the myspace home page, or login screen? Is it even the real myspace URL in your address bar?
And perhaps one of the more important ones is, does this only happen when you try to log in to FB? If the rest of your internet activity is ok, I'm wondering if it's not a virus, but a phishing attempt. If the URL's look suspicious, then that would be my guess.