Can't share folder

I recently set up my D-Link DIR-655 wireless router. It works fine. I then set up file-sharing between my Windows XP SP3 desktop and my Windows Vista Home Premium laptop. Both computers can share files via my desktops "shared documents" folder and my laptop's "public" folder. I have a 500GB external HD plugged into my desktop computer that I'd like to share with my laptop. I right-clicked the drive and clicked "Sharing and Security." I created a New Share with Full Control for "EVERYONE." The hand now appears under the drive's icon. I can view the drive from my laptop but when I try to enter any of the subfolders, I get an "access denied" error. I figured I may have to share each subfolder individually. I gave Full Access to one subfolder to try it out and I still get the same "access denied" error and I can't enter the subfolder.

My desktop uses McAfee's Personal Firewall but I have the 9 ports open for file-sharing that Microsoft lists. My laptop uses Windows Firewall.

Do you guys know what could be causing this? Thanks.