i understand what ure trying to do, but with that what ure trying it wont go…
This is to make subnetting a bit more understanding (if this is wrong, somebody correct me please): At first, you chose /30 (255.255.255.252) subnet, wich allows a maximum of 3+1=4 hosts (252 in bin is 11111100, so u have only 2 bits for hosts), i suggest u to use /28 (240) or smth like that, because i think u have more than 4 wifi clients a ? ;)
So the easyest way would be to: 1.) But a atheros based wifi card ; 2.) But a Linksys wrt54gs, flash it with dd-wrt, set it in ap mode, disable wan, connect it to lan, set it up, and select AP isolation...