hoeflake,
There isn't a attribute for what you are looking for in the AD schema. However, that is not to say it cannot be done.
I would tackle this in one of two ways:
Create a login script that updates the extensionAttribute property with the computer name the user is logging on to.
or
Add a property to the schema called "LastWorkstationLogin" or some such(that may be too long, but you get the point) and update the property with a login script.
I tried to think of a way to do this without a login script and I could not come up with anything. Perhaps auditing, but if you were auditing a large group of users you could be talking heaps of data.
If you need help with either of the above I can provide detailed instructions. Word of warning: Once the schema has been modified(option 2) you CANNOT undo the modifications unless your rebuild your domain controllers.
Hope this helped.
Roger