I just got it to work after fiddling FOREVER with it. Try this out:

1. If you're using Web Pro, one problem might be the OS X Firewall at System Preferences > Sharing. Web Pro uses funky ports, 8827 and 8775, probably because it was developed for using GPRS phone connections and not computers. So I added a new description with these ports to the Firewall and turned it on. I think the host address, webpro.palm.com is responsible for sending the pages to these ports. These ports are documented on this Palm web page in itty-bitty type: http://www.palm.com/software/webbrowserpro/ I wonder if Palm will set up a host for regular http ports, and then we'll get fouled up all over again, hmmm...

2. pppd sends its messages to /var/log/system.log, so I went there to see what's up by doing a "tail -f /var/log/system.log" while I invoked the ISharing script with sudo from the command line. There was this bit of consternation:

InternetSharing[668]: InternetSharing starting
InternetSharing[668]: no primary service specified, exiting

So I commented out the Internet Sharing startup lines in the script with "#"s so it looked like this:

# ConsoleMessage "Starting Internet Sharing"
# /usr/libexec/InternetSharing

Then I used the gui based System Preferences > Sharing > Internet to share the connection. Check the "Share the connection ..." box, and agree to the drop window that says your ISP is going to sue you if you turn this on. I turned it on before invoking the IShare script from the command line, but I don't think it matters what order you do it in.

3. I saw some board messages from guys trying to get it work over a phone, and they suggested substituting the IP address for webpro.palm.com (63.97.179.33) in Web Pro's (menu) Options > Preferences > Advanced. That eliminates the potential DNS problems with the host address, anyway.

4. The connection should be working even if your funky ports are not open, because it should still be active for certain services. You can figure out whether your connection is working by using ping from within your Palm. Go to Prefs > Network > (your Service name) > (menu) Options > View Log with the connection active. Scroll to the bottom of the log and you can test ping there. Grafitti in "ping 63.97.179.33" return (downward left slash, not the Done button), and if your connection is talking to the outside world, it should have one line that says "Pinging 63.97.179.33 with 32 bytes of data:" and then it should return "Reply from 63.97.179.33: bytes=32 time=110ms TTL=125". If it times out, then you are not talking to the webpro site at the very least. If it works, I would ping a non-IP address like apple.com to test your DNS lookup. If it works there, then both the connection and your DNS servers are working. Beware that I got errors from some sites I pinged, including macosxhints.com, probably because they set up their ping services strange.

5. This issue didn't affect me, but it might be helpful for you: I'm on a home network, and a buddy said pppd might have trouble connecting between my Mac's 192.168.1.100 address and 10.0.1.201 in the instructions. So he suggested I assign the remote address somewhere in the same range as my Mac, so I used "192.168.1.100:192.168.1.101" instead of ":10.0.1.201" in the pppd line for the ISharing script. Didn't turn out to be a problem for me, but you might try it. And yes, the pppd options have to be on the same line as the command.

Hope that helps. I did a lot of other troubleshooting things that I don't remember anymore, so if this doesn't work for you, let me know and I'll try to think back on what else I did.