Local cached credentials

Start > Run > control userpasswords2 > Advanced > Manage Passwords

Or, alternatively:

Start > Run > rundll32.exe keymgr.dll, KRShowKeyMgr

Domain credentials

Start > Run > Regedit
HKEY_LOCAL_MACHINE > SECURITY > CACHE
By default only SYSTEM account has full access to this directory.
Add administrator to SECURITY key permissions
OR
Start Regedit as SYSTEM account
Set values NL$1 through NL$10 to 0 (zero)
IMPORTANT: If you delete values NL$1 through NL$10 completely, Windows will stop caching domain credentials!

Windows XP