To share the printer have a look at http://support.microsoft.com/kb/325860
and skip to "How to Share a Printer". You've got three different client OS's but the process should be the same - go to control panel, printers, then add a network printer.
To share files have a look here http://support.microsoft.com/kb/324267
. On your client computers, right click on "Computer" and select 'map network drive'. Then just enter the name of shared folder you set up earlier in the format \\computer_name\share_name. For example \\server2003\shared stuff .