authenticating in parent domain by using child domain user?

Question

I created a child domain and trying to login on parent domain with a user of child domain.

I am doing login attempt on Windows Login Dialog at PDC of parent domain.

Login is failing as parent domain could not authenticate user of child domain.

Is it possible to login in this way? If yes, the how can i achive it?

Notes:-

Both are Windows 2003 domains. child domain is direct child of parent domain. There is 2-way transitive trust between child and parent (created automatically).