How to log-on a windows xp user

[C# Programming]

Hi there.

I'm trying to write a c# code that will automaticaly initiate a user login, if the user is logged off for a given period of time.

I've tried using the ADVAPI32.DLL's function LogonUser, but apparently that is used for impresonation (am i wrong?).
So, how is that done?

In addition, i failed to find a way to check if a specific user is logged on or not.

Any idea?

Thanks,
SummerBulb