Well, I would say that is still your best method of getting notifications on your system. As you will be pissing about trying to find earlier versions of plugins, which are probably not available by now, to get Growl/Growlmail working.
What mail provider do you use? As there are a couple of third party Gmail notifiers available. Only problem of course, is whether they will work with 10.6.8.
Edit:
Growlmail 1.2.5 is the version that works with Snow Leopard.
https://code.google.com/p/growlmail/downloads/detail?name=GrowlMail-1.2.5.zip&can=2&q
So install early version of Growl, and follow this:
http://growl.info/documentation/appconfigs/mail.php
…and it might work….might not, though.