I've had this problem with GNS3 for a long-long while now. For whatever reason, my install doesn't enjoy working w/ Lion. Attached is a screenshot using the install base and OS version listed in the subject line. If this is an easy fix, I would appreciate some guidance, if not, I'm sorry for the extra engineering hours I've created:

http://i.imgur.com/uoRtS.png

Here's a fun one: Turns out, what I thought were uncompressed images, were in fact, not uncompressed. So, after doing that, everything is solid. Many apologies!