According to http://www.aircrack-ng.org/doku.php?...3d85315de9a081
"Only rt2500, rt2570, rt61 and rt73 can inject and monitor. Also see Ralink chipset comments later on this pager for important concerns."
The driver that it says to use either the beta or the CVS hourly tarball
I recommend that you try the http://rt2x00.serialmonkey.com/rt61-cvs-daily.tar.gz
this one should do the trick