After searching around for a while and finding that integrating vim and aspell was very easy, I tried the same with gvim. There seemed to be a problem wih the terminal type and the curses interaction. Creating this map in vim (via the .vimrc file) works fine if you run vim within Terminal.app or iTerm.app and have aspell installed (via Fink in my case:
" run aspell over selected text
map ^T :w! /tmp/aspell^M:'<,'>d^M:!aspell check /tmp/aspell^Mk:r /tmp/aspell^M
However, once the GUI for vim is running, the interaction with aspell was pretty useless. So I hunted around for a while and tried launching Terminal.app with AppleScript and telling it stuff, but I failed to get anything really useful to happen. I also found some threads on vim having an internal spelling function. Also, vim version 7 is around the corner so I could wait. But I can't. So, I came up with the following little solution. Basically, it runs an xterm with aspell running in it.
First the vim map. You put this into your .vimrc or .gvimrc file, depending how you're set up.
" run aspell over selected text
map ^T :w! /tmp/aspell^M:'<,'>d^M:!xterm -e aspellit^Mk:r /tmp/aspell^M
Rememeber that ^T is entered using Control-V then Control-T, and the ^M is entered using Control-V then Return. Now the code for ~/bin/aspellit. Make sure ~/bin is in your PATH environment variable, and then put the following code in a file called ~/bin/aspellit:
#!/bin/bash -i
tput reset
/sw/bin/aspell check /tmp/aspell
Remember to make it executable by typing chmod +x ~/bin/aspellit. Now simply highlight what you want spell checked using V, then hit Control-T and an xterm will pop up running aspell over the selection. You can use this idea to run any app that requires curses interaction under gvim.
Mac OS X Hints
http://hints.macworld.com/article.php?story=20060117204954733