Vista and Networking

I have an XPS410 with Vista and 4 other machines with XP. They are all networked thru a Netgear router. I can see all the machines on any machine. I have marked the 2 drives on the Vista machine as share but when I try to access either of them from another machine, I get a "not permitted" message (not exactly the wording of the message). I can give set every folder as share and can then access them. This is a really dumb way to have to do it. Is there a reason why the drives (or partitions - however you want to refer to them) when set as shared can't be accessed directly and not have to access each folder individually??  So far I think that Vista is pure garbage........