Cannot Get XP Desktop- Laptop Network To Work

I have spent the better part of two weekends trying to get my XP w/ Service Pack 2 desktop to network with my Vista Home Premium laptop. Both computers are in the same workgroup (WORKGROUP). I have turned off all firewalls, both software-based and on my router. On the XP computer, I have installed the LLTD protocol. The XP computer shows the Vista computer in the workgroup, but when I try to access it it tells me it is not accessible because I "might not have permission to use this network resource."

In Vista, the XP computer shows up in the Network Map, but when I pass the cursor over it, it stays as an arrow; it does not change to a hand. Furthermore, in the Vista Network window, it shows the router and the Vista computer itself, but not the XP computer. I also cannot access the XP computer directly by typing \ and its name. Each computer is able the ping the other. I am using a Linksys WRT54G-TM router. I am an administrator on both computers.