That is what Windows Terminal Services provides or you might consider VDI.
You can't get a multiple users accessing the same VM. You would need to have a unique XP VM for each concurrent user.
Based on my knowledge, you could achieve your purpose by following method.
Open the Windows XP Mode and create a new user account with a password.
In XP mode, click start button, then click Control Panel.
Select User Account in the this panel.
Then click Create a new account and type a name of the new account (for example: Test).
Choose the Account type, click Create Account.
In User account, please click the new account and Create a password.
If the new user account will be auto log on when running XP mode, please go to Credential Manager in Windows 7 and delete the Credentials of the new
account and check the result.
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