Problem Sharing Between XP and Vista

I have a problem similar to but a little bit different.

We have a combination wired/wireless home network in my house, consisting of
4 computers, all connected through the router which connects directly to the
internet. The configuration is this:h
Desktop1 - connected directly to router, running XP
Desktop2- connected directly to router, running Vista
Laptop1 - connected wirelessly, running Vista
Laptop2- connected wirelessly, running XP.

As of right now, Desktop 2, Laptop1 and Laptop 2 have no problems sharing
files with each other.
Desktop 1 can view all the other computers shared files, but Laptop1 cannot
view any of Desktop 1's shared files. I consistently get a "denied access"
message.
I don't know if the other computers can access Desktop1 (they aren't my
computers). It's most important to get Laptop1 and Desktop1 to share files.
All computers have shared files/printers on, with password protection off,
and I've gone through the network wizards over and over.
I should mention that Laptop1 can *view* Desktop1 on the network. It sees
it, it knows it's there...but the Desktop will not allow access, even though
the files on the Desktop are set to be shared. I also tried turning the
firewall off, and it still would not grant access. None of the other
computers are having issues...there's go to be a solution to this, I'm just
not finding it.