Logging into workstations as the user, but without their password

Here's the deal. I work for a small company where we have traditionally kept everyone's password on a list in a lock box. We often have to work on someone's machine when they're not here. We have a Windows 2003 Active Directory Domain w/all Windows XP SP2 workstations.

The concept of resetting a password makes everyone upset, so we keep the same passwords for 6-12 months right now.

I'm now looking at changing this policy to changing passwords every 3 months using the built in password management features of Group Policy.

I really need a way to access someone's computer as them to troubleshoot problems without resetting or knowing their current password. 90% of the problems that my users run into are issues that can only be seen when logging in as them. We rely a lot on the convenience of working on computers when people are out of the office.

Is there a way to go about doing this?

Thanks!
Greg