I'll quote the important part here in bold.
They are all connected to a workgroup. The two Windows 7's can see and talk to the XP Pro and Windows 2k, Both Windows 7's SEE each other XP Pro, Win2k. Both Windows 7's have their drives shared, however they do not show that the drives are shared, a user name and password is allways aked for.
OK, to properly share entire drives you need to set the regular permissions but also you need to set the Security on the drive itself in order to share the entire drive. This is an extra step because sharing an entire drive is considered to be a security risk. You would be better off sharing the entire "User folder" instead.
To share the entire drive:
Open My Computer -> right click Local Disk D or which ever drive letter your drive is using -> select Properties -> select Security tab -> click Edit button -> click Add button -> enter the name of the User you want to set Security permissions (it is the same user name you've set the sharing permissions for, ex. Everyone will set the read permissions to every user. Put check marks in the boxes for full access and control -> click OK hit apply-> select the desired permissions -> click OK -> wait while permissions are set -> and your Done.
Reboot all machines then try to access the drives.