Yes it is. I believe that AD has nothing to do with your current problem! (correct me if I'm wrong folks)
In any case, right click on 'My Network Places' and select 'Map Network Drive'
In this dialogue, as the drive to mount, type \\computername\c$
The click the button to use alternate credentials and type in;
computername/username (where the username is a valid user with appropriate privelidges for that machine) and enter the password.
This should explicitly provide a different username to guest, and bypass that annoying message.
Sorry if these instructions are a little vague, I'm stuck on NT4 here and all this information is coming from memory!
Good luck... hope this helps!
Terry-Lee Blay
MCP, A+, Net+, Server+, APS, IBM Thinkpads/Portables