Simplest way would be to just add a cheap WAP (Wireless Access Point) to your existing router/hub/switch. I've had good luck with the D-Link DAP 1360 on the consumer end, but the much cheaper TP-Link ones work just as well for the most part. Or simply buy an all in one Ethernet router with wifi built in and skip the WAP portion of it. I highly recommend any of the ones that are capable of running DD-WRT firmware, like the Linksys WRT54 series.
Creating an ad-hoc network via a Windows PC is not terribly difficult, however.
I find it to be unnecessarily complex, though. Such ad-hoc networks are more intended for one-off on the fly access, I've always found it extremely redundant to have to have a PC/laptop on at all times to serve out the wifi when a WAP can be found for under $20.