These seem to be quite expensive to buy and not too easy to find on their own, they are starting to find their way into modem routers, so that may be a better way of buying but if your happy with your present setup and need to have wifi printing to save having a pc as an always on print server then this may be for you.
For £1 more you can have a parallel port one from the same company.
The TEW-P1UG is a print server that transforms a stand-alone USB printer into a shared network printer. The TEW-P1UG provides IEEE 802.11g 54Mbps wireless interface for integrating into existing wireless network. The TEW-P1UG is designed for virtually all printers equipped with USB 2.0 compliant printer port and it is an ideal network solution to convert conventional USB printer into a shared resource on the network. Features: Wi-Fi Compliant with IEEE 802.11g and IEEE 802.11b Wireless