Don, just to expand on what I mentioned earlier and to help you understand what's going on: When you install Windows XP, the default user is called "Administrator" and it is enabled on all XP computers. So, when you access one XP computer from another one over the network, you probably connect as "Administrator" and that name is recognized on each of your XP computers and is granted full access, as long as you use the same password, or no password at all.
On Windows 7, the "Administrator" user name exists too, but it is disabled by default! Instead, when you install Windows 7, a new administrative user is created, e.g. "Don". You can quickly check which user names are configured: On your Windows 7 computer click Start, right-click on Computer and select Manage. In the Computer Management click on Local Users and Groups and then double-click on Users. You will see all user names currently configured on your computer, including disabled ones. You will probably see three names: Administrator, Guest and your user name (e.g. Don). The first too accounts are disabled (right-click to check their properties), and the only enabled user is "Don" (or whatever name was entered during the initial Windows configuration). The problem is that "Don" is not recognized as a known user name on your Windows XP computers. Even though you are an administrator on your Windows 7 computer, you are treated as a guest user on all other XP computers and because of that you are either not allowed access at all or you are granted a read-only access as a guest user.
The reason you can't access your Windows 7 computer from your XP computer is different! There are actually two reasons: first, as I mentioned above, Windows XP user "Administrator" is not recognized as a valid user name in Windows 7. Second, the network file (and printer) sharing is disabled by default on Windows 7. You need to enable it if you want to share any files!
Hope this helps!
