According to HP Spec sheet
You computer does not have a wireless card installed. To Add wireless capability you need to add a Wireless network card, or a USB wireless adapter. This
one from Rosewill is relatively inexpensive and works well With windows XP. You will need to install it inside the computer in an open PCI slot which you should have 2 available. You can choose a USB adapter which is easier to install but IMO do not work quite as well. Similar prices can be found at Walmart they carry linksys and Dlink which are both good manufactures.
Systems and Network Engineer
Certified CompTia Network +, A +