Source code from the "Lisp manipulation of C structures" presentation has been contributed to WikiBooks:
Start here: http://en.wikibooks.org/wiki/Programming:Common_Lisp
The section added: http://en.wikibooks.org/wiki/Programming:Common_Lisp/Files_and_Directories/C...
Please feel free to annotate and make further contributions there, as that's the whole point!
If you're looking for the full code used in the presentation, it's on my site: http://play.org/lispsea/c-struct/ and has been cleaned-up based upon our discussions.
Thanks again to the fellow with deep knowledge of SBCL internals! (Sorry, I didn't catch your name.)
-Daniel
PS - the next meeting is announced on our wiki page: http://wiki.alu.org/LispSea