The XP feature known as "fast user switching" is disabled when a computer is a domain member. This is a Windows design constraint for security reasons.
XP computers cannot be a member of a Workgroup. Workgroups are a legacy feature of much earlier Windows systems and was made obsolete with Windows 2000. While workgroups can make finding other related computers easier, this is merely a cosmetic effect that is easily overcome.
In brief, when a computer is not a member of a domain, it's security is similar to XP Home Edition (which can't be a domain member). So essentially, by not using XP Professional in a domain, you've converted it into an insecure consumer toy that can never be HIPAA compliant.
Since domain membership implies a level of trust, the members of a domain must have trusted software prior to becoming a domain member. That means we can only add computers that have have been imaged
(have a hard drive with XP Professional and applications pre-installed and configured with secure settings) as members of the Waisman domain.