I've had problems for a while with Wireshark crashes on Mac OS X 10.6 (“Snow Leopard”). I finally tracked it down today.

1. Install XCode

2. Use this dtrace one-liner to watch all the files being opened on the machine:
dtrace -n 'syscall::open*:entry { printf(“%s %s”,execname,copyinstr(arg0)); }'

3. Found where “CrashReport” ran in the output, and then looked back from there to see what files had been opened. I identified these files, and removed them:
~/.fonts.cache-1
~/.fonts
~/.wireshark
~/.wireshark-etc

(For you Finder users, these are all hidden files in my home directory.)

One of those must have had something bogus in it, because wireshark started up the next time.