I installed GTK+ 2.2.4, GIMP 2.0 pre2, and immediately added the GIF plugin 
and the plugin pack before starting it for the first time. Then after 
starting, I had to enter several options (e.g. the TEMP dir); then GIMP was 
about to start for the first time. In the middle of the initialization 
process, progress bar near 50%, during the stage "Fonts", it crashed with 
the following output in the debug window:
__

gimp_composite: use=yes, verbose=no +mmx +sse -sse2 -3dnow -altivec -vis

(gimp-1.3.exe:832): GLib-CRITICAL **: file gconvert.c: line 498 (g_convert)
: assertion `str != NULL' failed
__

Even the optimizations are suspicious: My AMD Duron supports MMX, ISSE, and 
3Dnow! - but not full SSE.

Also I wonder if I could help you by creating a verbose debug log - if I 
just knew how...