While it's possible, wifi cards weren't meant to operate in an ad-hoc fashion like that, they really are designed to operate with a wireless access point of some kind.
Things would be a lot better if you picked up an 802.11g router and used that for communications between your systems. You can pick up the D-Link DI-624 (the router counterpart to your wifi cards) for about $80 last I checked. The DI-524, which doesn't have the 108Mbps mode capability is around $50 as I recall. But any 802.11g router should work, and will make your life a lot easier.
I managed to established an ad-hoc connection between two computers, using static assigned IPs;
Dell Inspirion running XP home with D-Link XtremeG dwlg650 pc card;
Home PC running XP pro with D-Link XtremeG dwlg520 pci card /w a dialup connection;
Sometime it works and sometimes it doesnt. Recently, my problem was that even though both comps have connected to a SSID that has worked before, my PC connects to the SSID, but one, or both comps says it connects to a SSID that has no name (but they connect at the same time so its not a foreign connection), obviously I cant access either comp from the other because of this (PROBLEM ONE).
I've used Network Stumbler on my laptop to see that thats the only connection available, and even then it detects the SSID as blank... but the PC says it connects to the SSID i named.
Also, when this has happened, getting online from my PC on the dial up failed, in the sense that suddenly i couldn't access any internet data (msn, IE) until i disabled the PCI card. (PROBLEM TWO)
Lastly as a mention, I access the net from the other comps (one other standard PC through a wired connection, bridged, that has worked with the others as well) using analogx proxy, but this hasn't been a problem in the past. I use it because I can't get windows Internet Connection Sharing to work at all! I've been able to disconnect the PC with the internet connection remotely from the other computer, as it detects the connection, but it can't connect still (IE cant get to any pages). PROBLEM THREE, but not as important).
Any help with any of these issues would be GREATLY appreciated!