There is an extremely valuable (and small) vim plugin slime.vim out there, with a nice description of the how, why and what at the author's site: http://technotales.wordpress.com/2007/10/03/like-slime-for-vim/
With this simple plugin, you can edit your code in a vim "worksheet" and send it over to *any* REPL (bash, gst, sbcl, vim, ...) that is running in a screen session.
For the impatient:

• Drop the plugin into your ~/.vim/plugin folder and restart vim
• screen -S gst, then in the session gst
• run (g)vim and type CTRL-c CTRL-v gst 0
• enter some smalltalk code and type CTRL-c CTRL-c
• see the output in the screen window

Good stuff.