I'm not sure what I did but Gimp stopped working properly.
I get "The procedure entry point g_ascii_strtoull could not be located in the dynamic link library libglib-2.0-0.dll"

I have even unistalled it and tried reinstalling it several times. I even tried another version... It's version 2.6.3.

I'd be happy with an old version that worked...anyone have any idea's what I can do to fix the mess I've made?

I don't think you did anything to mess up your gimp. I had exactly the same
problem and I don't think I did anything to cause it either, so it must have
been one of the numerous vista nightly upgrades that caused my gimp to no
longer function.

Anyway, the problem is apparently caused by some very old DLLs that exist
within your C:\Windows\System32 directory. If you go in there and look for
libglib-2.0-0.dll, you will probably find a copy that was placed there when
you installed a previous version of GIMP or some other application that used
GTK or GLIB. I apologize for not being able to list them all, I trusted Vista
to retain them all in the recycle bin when I deleted them, but they appear to
have been lost forever. Originally, I renamed this libglib-2.0-0.dll file to
libglib-2.0-0.dll.bad but that resulted in a complaint about some other entry
point not being found. So then I noticed that there were 4 or 5 other files
that all had the same date and appeared to be part of the same original glib
install, so I deleted the group. That was careless and I apologize because I
could have just as easily moved them into a temporary directory or renamed
them, but anyway, that cured the problem. With those files gone, GIMP is able
to dynamically link with the DLLs that are supplied with the installation and
everything runs fine. Maybe somebody else that has the same problem can repeat
the experiment and supply the list of files that need to be removed from your
LD_LIBRARY_PATH ( or whatever they call it under windows ).