Wireless File/Printer Sharing

Hi folks, I'm having a problem with file/printer sharing over a wireless network and am hoping someone here can help :

I have two computers that access a wireless router wirelessly (the router doesn't have anything actually wired into it). They can both access the internet fine independently through the router.

I tried using the "set up a home or small office network" and everything went fine - I was able to share selected files and use the printer from both computers. However, it only works intermittently - sometimes i will be fine, other times only one computer can access the other, sometimes none at all. If it doesn't work I get a "network path cannot be found" error.

One of the computers is XP Pro whilst the other is Home and both have ZoneAlarm installed which may be problems but I don't understand why it works sometimes but not others - I think it's actually more frustrating than not working at all!

Any help, before I destroy something, would be really appreciated!

dhill