Wireless networking difficulties.

The following computers are connected via a Gigabyte GN-B46B wireless router:

-HPVECTRA, a desktop running XP Pro, and connected to the network with Cat5 cable
-CELERON, a desktop running XP Pro, and connected to the network with Cat5 cable
-JIEHAN, a notebook running XP Home, and connected to the network via WiFi
-CKF, a notebook running XP Home, and connected to the network via WiFi

All computers are able to access the internet through the router.

The 2 wired desktops can ping and be pinged by all the other computers. However, the 2 wireless notebooks are only able to ping the wired desktops, and not each other. The wireless computers are also unable to share files, play network games, or do any of the other things that a networked computer ought to be able to do, with each other. There is no problem doing any of these things between a wireless and wired computer, or between the 2 wired computers.

I tried connecting each of the notebooks in turn to the network by fast ethernet instead of Wifi, and it turns out that once one of them is connected to the network by wires, it is able to ping the other without difficulty.

This seems to be a problem with the wireless end of the network. Any helpful suggestions?

I've solved the problem. For anyone who's interested, I used fixed IP for the wireless computers, and excluded those IP addresses from the router DHCP. The exclusion is vital, or you still can't network.
Seems my DHCP wasn't properly configured, but the router doesn't offer full features so the only thing I could do was not use DHCP for those computers. Which is quite unfortunate, considering that it's the notebooks that could really benefit from DHCP.