Have you used the wireless on this laptop before?
Wireless b was optional on that model, so it may not have the wireless module, in which case you would need to add either a wireless card or usb wireless.
Check the whole model number-- it would end in something like WJ510 (the W indicates the type of cd/ddvd drive, the J would mean wireless (if anything else then no wireless), the 51 or 25 indicates amount of memory, and the final 0 or 2 indicates the operating system.