A Dutch website known as System 6 Heaven has created a page of tips for sharing things between older Macs and Macs running OS X. One of the little tidbits on the page explains how to enable AppleShare over AppleTalk, thereby allowing your System 6 Macs to see your OS X box directly on the network.
If you have some older machines that you'd like to network, check out the System 6 Heaven tips page for some good pointers.
Mac OS X Hints
http://hints.macworld.com/article.php?story=2001122310324523