Win 7 file sharing

I have a Windows 7 Ultimate 32 system and a Windows XP Home SP3 system. After a lot of blind alleys, I've got them connected through a Netgear wireless router physically connected to the Win 7 machine, and a Cisco USB network adapter on the XP machine. And I've managed to get my two printers on the Win 7 machine accessible to the XP machine. Now I'm working on sharing.

Since I am the only user of EITHER machine, I'm not particularly concerned about access control in either one. If there were a simple checkmark to say "Let everything on both computers be accessible from EITHER computer," I'd check it. But for now, what I've done in an effort to get started is to share the D and E drives on both machines. I've gone through the steps to share the drives, acknowledged that I understand the security issues (on the XP machine), and the drives on both machines have names.

Now for the problem. From the Win 7 machine, the drives are listed under the XP machine under NETWORK in Windows Explorer. And I can click on them, expand their folders, and access their files with no problem. However, on the XP machine, under Network Places, under ENTIRE NETWORK, the drives are listed--that is, it shows D on Office (the XP computer) and D on Dell (the Win 7 computer). Same for drive E. However, if I click on the D on Dell drive, I get a message that says \\Dll\D is not accessible. You might not have permission to use this network resource. Contact the administrator of this server to find out if you have access. Access is denied.

Well, I'm the administrator of that server, I guess, and I thought I gave me access. However to be sure I went back to the Win 7 machine and went through the Permissions options on the D and E drives. They were both listed as Read for Everyone. So I changed them both to Full Control for Everyone. But that didn't change the Access Denied box on the XP machine. (I didn't really think it would, since it would not let me access the drives at all, even just to read). There is also listed on the XP machine, a folder named users on Dell, and it has two subfolder, default and Public. Those folders can be expanded without a problem.

Anyone know what I'm missing here?