In order to boot PXE you need:
1. NO security enabled (the wifi card can't use wep or wpa during boot...)
2. TFTP for the PXE Image (Trivial File Transfer Protocol)
3. DHCP with PXE BOOT enabled...
the big problem is #1. You CAN do it, but it would be a HUGE security hole as anyone walking by could log into your network.
Also, with wifi, the network bandwidth is SHARED across all nodes, and the maximum speed of the network is capped at the slowest node's speed.
ie: if you have 802.11g 3 nodes, and 1 801.11b node, ALL nodes share MAXIMUM 11mb/s which really slows traffic down.
Wired is your best bet.
HTH,
Dan