well i don't know if you can actually do this in fruity. i don't use the program that much but it's a pretty advanced feature in music programs and i'm sure i'd know about it if you could. if i wanted to take a riff and make it to a certain tempo, i'd use sonic foundry's acid. then you'd export the wav and use it in fruity at the right tempo.

but then again, i don't know if acid imports rm files...

rm is a really bad format. your riff will sound really bad in quality. why the hell you'd want to use an rm file i'll never know :? stick with wavs or aiffs... mp3's are ok too but often really compressed and therefore loose alot......