Here's a short intro to sharing printers and how to tell if its a network or local printer:
There are two methods of installing printers. If a printer is physically connected to a computer by a cable then it is locally
installed regardless of whether or not the printer is shared.
If a printer can be assigned an IP address, has an ethernet connection (plug for a network cable) or can be connected to via wireless networking then it is a network printer even if it is directly connected to a computer.
In order to share a locally connected printer, the computer the printer is physically connected to must be turned on and the operating system must be running for the printer to be available to print.
In order to share a network printer, the printer must be connected to a network at all times. It does not matter whether any computer is turned on or not.
Here's a Microsoft tutorial on how to share items between Vista and XP:http://technet.microsoft.com/en-us/library/bb727037.aspx