How can I incorporate users in to my forum tables? (UserIDs are weird, I can't use Names, and I don't want to modify the Profile Tables)

So I'm making a website that's going to use forums, and I'm not completely sure how to incorporate profile into it... I have a Topics table, a Replys table, and of course the ASPNETDB default tables. (Both of those tables are in the ASPNETDB, just to keep everything together). I have a mechanism to display topics in the table, by displaying an Author name, that's actually assigned as data in the topics column, and the post name and description. Ideally, I could just use the Profile name as the author through an FK relationship (or something like that) OR I could, when the topic is assigned through a DetailsView, add the name of the current logged in user (the page is only accessible to those that are logged in) to the entry when I put it in. 
I don't know how I should do this, and I'm a pretty beginnery beginner and so if there's some better solution that I don't know about plea ...