I'm not sure what would run well on a Tiger Pismo. I know Tiger didn't feel that great on my G3 iBook and that had 800MHz and 640MB RAM.

Here's a couple of basic VST hosts I found:

http://www.refusesoftware.com/products/feature/3

http://www.440audio.com/en/software/v3126-The-Lone-Roger-MultiVST-Shell/

And there's a few more listed here. If you have a look through the site you might find some more cool stuff.