As far as I know, you cant map a drive to a shared folder with one username/password on the same server as another mapped drive with a different username and password.
If you are doing it programmatically you can add multiple credentials to the credential cache, that would allow you to authorise yourself with multiple permission sets.
I've always been able to map drives using the same username and password to two different servers.
For example
net use x: \\server1\shareFolder /user:domain\username
net use y: \\server2\shareFolder /user:domain\username
You can omit the /user section if you want the network share to be mapped as the current user.
You can have as many network drives as you want on different machines as long as you have enough drive letters.
alternatively you can use the unc path \server1\share1 and \server2\share1, if your username and password which you are not currently logged in as do not have access windows will prompt you for a username and password.