Redirect links

I would like to redirect the login and register links on my blog so that instead of taking me to the wordpress user login/register page, they instead link directly to my phpBB3 login/register.

Reason: I have a bridge between the 2 databases but it only works from phpBB3 registrations; besides I would rather keep the site cleaner with one page (the phpBB3 one) used for all user logins.

I am unsure of how to effect this redirect on the wordpress end – I imagine I will have to change a php script somewhere?

Simple instructions on how to achieve this will be appreciated.