Make sure both the laptop and the desktop have the same Workgroup name, right-click the My Computer icon on your desktop, choose Properties > Computer Name > "Change" button. In the Computer Name box, type in a name for the computer, if you're on the laptop, name it something like "laptop", if on the desktop, name it desktop. In the Workgroup box, name both the laptop and the desktop with the same workgroup name, usually something like "Home".
Then on the computer the printer is connected to (usually the desktop), go to Control Panel > Printers, right-click on your printer's icon, choose "Sharing" and select the "Share this Printer" option, give the printer an apt name if you wish.
Then on the laptop, go to Control Panel > Printers and click the "Add A Printer" option and follow the wizard to detect and add the shared printer. Your firewalls might interfer with the detection, so temporarily disable them.