I would get a mac if I were you, but that could be just cuz I'm a mac addict. They're VERY reliable though, but I don't think FL works on it.
You can get Reason, Pro Tools, Digital Performer, Nuendo, Logic, and a whole bunch more programs that are sick. Also the other propellerhead software along with Reason, like ReCycle, ReBirth, and all that stuff.
I have a powerbook G4 and it's NEVER crashed on me, even while having tons of plug-ins active in pro tools, with reason working along with pro tools in rewire mode.
All I have on this machine is 768MB ram, with a 1.5GHz processor. But the mac's processor is much faster than a pentium. I could be wrong about this, because it's second-hand knowledge, but my friend said his powerbook 1.5GHz was faster than his Dell 2.5GHz laptop, because he ran calculation tests. That's on him tho... not my info from personal experience.