Hi,
A better way to accomplish this would be to modify the portal logon page and add a check-box and a link to the Terms and Conditions (which would open in a popup). Login should only be allowed when the user accepts the T&C by clicking the check-box.
In your case, since you are using WD ABAB, I believe the re-direct to /irj/portal.... will not work unless you hard-code the host-name and port of the portal instance.
Regards,
Rajiv