custom error message for incorrect login

[DHDesign]

i have designed an intranet that utilizes vbulletin's user system...i have my own login form and once a user puts in his/her credentials, they go to an internal customized page (through which they can also access the forum).

but, when a user puts in incorrect info for their user/pass, it takes them to the vbulletin msg (using their style)...i want it to go to a customized error page or just reload the login page again.

any advice?
thanks