Vista/XP file sharing problem.

I have two desktops, one running XP Pro SP2, and the second is running Vista
Home Premium which I installed last night.

Both machines are members of the same workgroup "Home" and the Vista machine
is named DESKTOP1 and the XP machine is named DESKTOP2.

On each machine, I have two folders in the Program Files directory that I
need to share. My Vista machine can access the folders I have shared on the
XP machine with no problems. I can see Vista's shared folders on my XP
machine, but I get permission errors when I try to open the folders.

When I try to share the folder in Vista, the "Share" button under Network
File and Folder Sharing is grayed out, all I can do is choose Advanced
Sharing. I'm assuming my problem is one of permissions, but I cannot find a
way to give permission to any user accounts on my DESKTOP2 machine.

Any ideas before I uninstall and go back to XP?