Block services (everything?) on WRT54G?

I'm trying to set up a WRT54G for open public access, but only allow certain services (maybe just WWWeb Browsing, for instance), but seem to have run into a problem.

I've got a Linksys WRT54G V4 running 4.20.7 firmware, and I seem to be having a number of problems. Igo into and :

First, there are only two available selections of services, shouldn't I have a list of things I can block?

Secondly, just to try it out, I'm trying to block Ping, but it comes up as ports zero thru zero, which is wrong (isn't it?)

Then, I fix the ping port to port 7 and enable it and I can still ping machines on the WAN side of the router.

Yeah, I could probably retry DD-WRT, but last time I followed the instuctions to the letter they didn't work, and that's really a rathole.

Also, if I only wanted to allow WWWebBrowsing, what do I need to allow for ports besides 80 (HTTP) and 53 (DNS). I'm not sure if I care if people can do HTTPS or anything else...

Has anyone made this work? I've got a couple of WRT54G V5s in stock, but they are unopened, so I'd rather keep them pristine...

Thanks!