You just need to install a Wireless Network Adapter (802.11g 54Mbps) in each PC.
For Desktops, either internal PCI or USB
For Laptops, either PCMCIA or USB
<<< And does wireless work ok >>>
Generally, yes, but a "wired" network will always be more reliable and, for file transfers, will be faster. The claimed speeds for WiFi connections are not realised in practice.