First, make sure that you have updated to 7.5.3 which is freely available on Apple's website. Next find the Classic-Open Transport switching utility and choose Open Transport. It will make you reboot if you have to change.
Now you have the same TCP/IP control panel that you should recognize the fields to enter. Go to Edit-User Mode and choose advanced. Now there is an Options button at the lower right. Click it and choose to have TCP/IP loaded all the time NOT on demand.
Choose your ethernet interface (your 630 does have an ethernet card installed with drivers -right?) in the drop down box of the TCP/IP control panel. Enter your information from the other machines including a manual address or DHCP. Close the panel and it should be able to get on the net. A reboot might be required, but not generally.