One router (NOT a modem/router. Be very careful to get a standalone router).
Two PCI wifi adapters, preferably with proper wired aerials for desktop positioning. Probably best to avoid USB adapters.
If your notebook lacks an Ethernet port (it should have one) then you MUST make sure that one of the desktops has an inbuilt Ethernet port. If not, you WILL need to add a PCI Ethernet card to provide a means of configuring the router. This is essential on first use and whenever you change wireless settings. For obvious reasons, you cannot change wireless settings when a wireless connection is running!