Hi, I searched this concern before cause I wanted to use wifi too in the office. I'm not sure where the thread that I read had been sucessfull but it did gave me the idea to set mine and get it working.
Basically I have LAN connection in the office, connected to my Dell Latitdue d600 and created ad hoc connection to my HTC Touch.
I opened network connections, and right click my lan connection, advance tab, and enable internet sharing using wireless connection, thats the only thing i did, after establishing the adhoc connection, IP address in Pc is the same, 192.168.0.1 and subnet mask is 255.255.255.0 hope you get it working. I dont have a smartphone to test it myself