Sharing a printer over a LAN without making a guest account

you don't say if you use WinXP home or prof version. In prof version, you can change the permission needed to print on this printer (on the Security tab). To make it possible to print without having credentials on that machine, you have to grant "Printing" to both "Everyone" and "Anonymous" (yes to both, that is a relic of WinNT times...). By default, only "Everyone" may print, which requires credentials for any account on that machine.

It does not have to be a guest account, you can also add a normal user account and add it to the lists of users who are not allowed to login (and not allowed to do almost everything else except read the WINDOWS directory and print).