I have similar issues when I attempt to use a shared file on my PC with my daughter's dell laptop. I've not found a satisfactory reason why it happens but I think that sometimes XP Home has problems with network sharing and it tends to lose track of the connections.
I've tried everything from rebooting both PCs, rebooting the wireless router, disabling the shares and re-enabling them to no avail. I've rebuilt the connections etc but no joy.
XP does not always refresh the list of available folders. For example, if I connect my laptop to my mate's network, his shared folders appear in my network connections. However, when I disconnect and then connect to my own network, the shared directories are still there, it simply tells me that the path can't be found when I access them. The only way to remove them is to delete the folders manually.
Sometimes the folders simply vanish from the network and other times, they're there but, as you say, you open them up and nothing appears, only the usual windows error message. The same thing happens with shared printers - they show up as being there but nothing happens when you print as it says the network resource can't be found.
I've literally spent hours trying to find why I can't access a folder only to find the next day that I can suddenly access them again. Most times now, I do nothing and for no reason I can fathom, it just starts working again. Something must be changing but I can't figure out what it is.
I've got an iBook arriving shortly (fed up using my daughter's dell) and so will post again if the same thing happens. I still think that networking on XP home is as stable as a three legged horse. I don't know if Pro is better.