there was a render problem with cs3 and 8-core systems that was fixed in an update (8.0.2 is the latest). so make sure you have the latest version…
there was also a post a week or two ago with similar issues… the problem was traced back to an older piece of audio hardware. if that device was disconnected, ae rendered fine. what kinds of extra hardware do you have (video/audio capture devices, etc)?
also, do you experience this problem rendering to all codecs/formats or just one specific one? and do you experience this if you were to ‘export’ the file as, say a dv stream, rather than render?
and, one last thing, has it always been an issue, or is this something new? if it is new, you might try running the disk utility (applications/utilities) and repair permissions and verify disk. maybe even remove the ae pref file folder (users/[username]/library/preferences/adobe/after effects). move the folder with the version number (like 8.0) to the desktop, start ae and try a render again.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW