Hi.
You might be able to get FL running under WINE (i don't see any major obstacles, but I've not tried my self).
I've been waiting with baited breath for an application similar to Fruity Loops to come out for Linux for a while now. I'd be very interested to hear if you do get it running (I'm not willing to pay for FL until I hear that it can be run under Linux/WINE).
Audacity can use VST instruments, and there's a couple of apps which do things like drum layouts for Linux, but there's nothing as powerful as Fruity Loops available for Linux at the moment.
You might want to have a look at Rosegarden (
http://www.rosegardenmusic.com/), but it's most probably not *quite* what you're looking for.
Dave.