prevent sleep so i can close my XBMC macbook

I've repurposed an older MacBook as my XBMC machine, and all is well except that I'd like to be able to close the cover and nt have it go to sleep.

installed the noSleep application but it acts oddly, it keeps it "sort of awake" ie network operations stutter, it's extremely slow to respond to remote controlling via VNC or the XBNC web remote. i open the cover back up and wham, everything is fast again. close it, slows to a trickle.

anyone else running XBMC on a mac laptop who's solved this issue?