Yes, it does fit the FX 5900, but you <b>must</b> use the optional fan. I have one on an ATi card and it rocks.
<A HREF="http://rmitz.org/AYB3.swf" target="_new">All your base are belong to us.</A>
<A HREF="http://service.futuremark.com/compare?2k3=2216718" target="_new"><b>3DMark03</b></A>