I am hoping someone can give me some help here.

I have a 3-computer network. All are using Windows XP SP2. Simple
File Sharing is enabled on all.

Computer 1 is a laptop connected via ethernet cable to a D-Link DI-524
wireless router. This router is connected to a cable modem.
Computer 2 is a desktop, connected to the network via a wireless card
Computer 3 is a laptop, connected to the network using a PCMCIA wifi
card.

I set up shares on drives on all 3 computers.

Computer 1 can "see" both of the others, and can access the shared
folders on them.
Computer 2 can "see" 1 and 3, but when I try to access them, I get an
error saying I don't have permission to do so.
Computer 3 can't even "see" the other 2. When I click on "view
workgroup computers," I get an error message saying the workgroup is
inacessible and I don't have permission to do so."

All 3 can access the internet.

I used the Windows network setup, and still have problems. I am at my
wits end.

Any help greatly appreciated.