The brilliant programmer responsible for installing that feature for us wrote up a little tutorial - he says:
"To add your blog RSS feed to your profile: Click "User CP" on the top menu and then click "Edit Options" on the left menu, then scroll all the way down and find the field called "Blog RSS feed", enter your RSS feed URL and in the next field called "Blog title" put the title you want to be displayed, for example I filled that field with "Codehead Webmaster Forums", you can say "My latest blog post" or whatever you like"

Give it a shot and if it's still not working for you just let me know and I can add it for you (you can send me your RSS URL via PM)

__________________