rev a 233 imac
i've got jaguar on a rev a 233 imac, and it's acceptable. i did bump the memory to 512, so that helps.
a lot like gotohamish, just above, i use photoshop elements, golive, serve a few php-based websites for development purposes, do a little java, whatever. things may take a bit longer, but they work. i play zero games, so i can't comment on performance in that area.
just install jag already! you can get the benefits of x, and if it's too slow you can always boot to 9. plus, when you (or your friend) gets a faster machine, you won't have to worry about getting familiar with x. you really can't go wrong. just beef up on the ram.