Simply call the SHGetKnownFolderPath
API function.
Since this function was added in Vista, it won't be declared in the library units that shipped with Delphi 7. So you'd need to declare it yourself.
type
KNOWNFOLDERID = TGuid;
function SHGetKnownFolderPath(
const rfid: KNOWNFOLDERID;
dwFlags: DWORD;
hToken: THandle;
out ppszPath: PWideChar
): HResult; stdcall; external 'Shell32.dll';
Now, since this function was added in Vista, attempts to call it on XP will lead to failures. So, I would recommend dealing with this by using CSIDL functions rather than the Vista known folder APIs.