I play in Gentoo 64bit all the time. I didn't do anything special, just compiled and installed Wine (winehq.org) and then stuck in the Freelancer CD like I was on windows. Installed FL, then FLMM, then Discovery. Logged on and it works fine.
I've even gotten it to work within a windows xp Virtual Machine (via vmware), and it wasn't laggy and worked fine, though there was a slight but noticable delay between moving the mouse and the cursor on the screen following suit. I doubt it was even half a second behind though, so only a problem when in real intense twitch fighting, like light fighter vs light fighter.
@ OP: Post your specific problem, and I can help you with it. Hard to help if I don't know what went wrong. If you are looking for specific instructions, drop to commandline, type "sudo apt-get install wine" to install wine, then install Freelancer using wine, run it, bingo there you go. Anything goes wrong let me know.
@ Death's Overture: Can you get decent FPS in other linux games of similar graphical requirements? What is the result of typing "glxinfo | grep direct" into the console? what is your FPS when running "glxgears" in console?
