First of all, is the G4 set up to always be at 192.168.1.103? Manual IP or "DHCP with manual IP" are required there (System Preferences...->Network), else it might not always be at that address.
Also, web sharing is usually at port 80 (is yours set up for something else?), FTP is at 21, VNC (remote desktop) is at 5900 (and 5901, 5902, etc. if you use multiple displays) - these are the default ports; you might use different ones. Also, beware of FTP unless you know what you're doing - it's pretty easy to hack into. SCP, SFTP, etc. are better options.
You need to be sure these ports aren't stopped by the Mac's firewall (System Prefs...->Sharing->Firewall) as well.