Well, Smoothwall says it will work with that set-up ...I would be real interested to see how it does.
On the other hand the memory and disk space may be a little lacking for snort ( especially if you want a nice GUI interface ).
In this case I would run that 133 on a Linux 2.4 kernel distro with NO GUI, minimal set-up, which is how I set up firewall boxes anyway. I've used similar boxes in the past set up this way.
But if you don't know Netfilter, maybe Smoothwall is the way to go, and as I said I would be real interested in how it works out. Then look around for someone discarding another box for Snort.