need some asp help

Hi guys

I'm working / fixing my site and need some help.

I'm using forum registration in order for users to view some pages which are only for members.

Now the thing is that if user is registered he/she can fill out some form to add its own message etc...
Up to now users had to write its username or name before submitting the form.
What I would like is that when user decide to write something his/shes forum username would be shown instead of writting the name into the textfield.

Example:

Title: test
Comment: comment, comment

Added by: Urko - my username

Hope you know what i mean
Thanks,