Unfortuately, VPN clients for the PPC are extremely rare. There are only a few of them out there and they're not free (nor cheap).
Personally, I've only used mobianVPN, which
was an excellent client. It was compatible with the Cisco VPN Concentrator 3000 server and free trials were offered by Certicom. Because they've left the market, you probably won't find any *legal* copies since you require a licensed certificate to run the program.
AdmitOne was another reliable product. But again, it was discontinued ealier this year.
Good clients available today include
Check Point and
SonicWALL, which I can't comment on. They go for around 50$ last I checked. There might be a few others I'm missing, but these are the most popular ones.
If anyone does come across a free VPN client for WM2003, make sure to drop me a line :wink: