lend a hand with regular expressions?

I've been fiddling with regular expressions and, well, I'm not that great at getting things the right way around so I figured one of you guys/gals would be able to lend a hand. I need a regular expression to check against user-submitted comments, so it needs to allow letters, numbers and punctuation.

I did a google search for examples but all I can find is "email validation" ones.. apparently users only ever submit e-mail addresses through forms ;)

If you could direct me to a decent resource (not php.net), that'd help too. All help appreciated!