Networking

Am using Windows Server 2003 Entp Edition.
When i try connecting to XP clients from Server using run cmd \\192.168.0.05\C$ it asks for Connecting to 192.168.0.05 username shows U36\Guest which is dulled out (cannot be changed)
and Password, when i try entering the pwd it says Logon unsuccessful. Have tried all pwd used in the office, but no luck. Can some1 help.