To make a laptop wireless, a signal is necessary, either available at a home network or any public Wi-Fi location, and a wireless card or built-in wireless connection is required for a laptop to pick up the signal.
How Do I Connect A Wireless Printer to a Wireless Laptop? Printers that can be networked will come with either a wireless adapter or a network adapter.
  Since the question states wireless printer then let's assume that it has a wireless adapter.
 You can then plug it directly to a wireless router or you can use it in what is called ad-hoc mode.
If you choose to use ad-hoc mode then be aware that printing will monopolize your wireless adapter in your Laptop.
There are some good step-by-step instructions at wikiHow;   "How To Set Up a Wireless Printer Connection".
Are all Laptops Wireless? Most laptops today (Oct, 2009) have integrated wireless, so you will not need to purchase a wireless adapter for the laptop.
How Do I Connect an Old Laptop to a Wireless Home Network? Depending on how old the laptop is it probably does not have integrated wireless as most new laptops do today.
  Assuming you already have a wireless home network setup you will need to add a wireless network adapter of some type to your old laptop.
 Even though there are a number of different wireless adapters, the two primary ones used today for laptops are either a PC Card, sometimes referred to as a PCMCIA card, or a USB wireless adapter.
The PC Card is about the size of a credit card and fits into a slot on the side of your laptop.
 Before you purchase make sure that your old laptop has such a slot.
The USB Wireless Adapter will of course require that your laptop have a USB port available.
  Before you purchase either adapter, make sure that it is compatible with your laptop's operating system.
Also, make sure the wireless adapter is Wi-Fi certified.
  Check the transfer rate and the adapter's range to be sure it will meet your needs.