Shared Workstation Auto login issue

We have many PCs running XP that have are shared workstations with a generic AD login. We have a program that requires the user to login to each site (different hospitals)to access them. These PCs can login to our facility but do not get prompted for a login for others. Any PC on the same network where a user logs in does get prompted and is allowed to login.
These PCs are generally locked down. We have unlocked them (removed completely from the group), but that had no affect.
The shared user account is set up in AD just like an actual user.
Any ideas as to why we can’t even get the login prompt to appear? Security tabs in IE are the same for all users.