hope you understand
Honestly, not a clue.
Look in the HELP file for the TITLE function... and I think, for credits, you want a rolling title
Along with the tutorials on the wiki (John's link, and be sure to see any and everything pertaining to Titles), if you can attach an example of exactly what you wish, it might help. I'm with Jim, in that I'm not quite sure I get the idea. An example would go a very long way to helping there. If you can attach a link to something like what you want, on say YouTube (use the little blue A icon with a chain besides it, to attach your link.
I think that what you want would be quite simple to do in PrPro's Titler. However, it might require the work in either a plug-in, or stand-alone program, like BluffTitler, or ProDad's Vitascene or Heroglyph. We'll talk more about them, if that is what you need. Until we "get it," we could just confuse you with a bunch of recommendations that would not help.
Good luck, and please let us see a link to what you wish to do.
[Edit] Here's a screen-cap of that button to Attach a link: