Interestingly, I find that my gaim (on RH) does not have this dependency. I checked this with "ldd /usr/local/bin/gaim"
So, I checked my local rpmfind http://speakeasy.rpmfind.net/linux/RPM/
for libgtkspell.so.0 and it came up with a bunch of possibilities: gtkspell, yank-gtkspell, yank, and libgtkspell0. Are you perchance using Mandrake? See if you have these packages installed or on your CD's. Perhaps you need to make a symlink for the binary to detect the library if it is already installed and the version of gaim you installed expects the libraries in a different location than it exists.
More information would provide a better answer. Perhaps give us the results of ldd <path to gaim>/gaim|grep gtkspell?