your question was already marked "Assumed Answered" but I didn't see a response.
Take a look at this chunk of code from Todd Geist, it's a pretty elegant way to do what you need with virtual lists instead of relationship driven portals.
You might also want to check out:
Hey Mike... great idea but don't you think he needs some basic understandings of relationships and native FIleMaker before he goes down this path.
David... you can achieve this in many ways. Mikes suggestion is solid... but may be a few steps away from where you are on the learning curve.
You could...as one option... have FIleMaker calculate the initial letters and using valuelists generate the alpha-buttons for you. left(surname,1) will give you the first letter of the surname.
When clicking on say "C" you could set a global field with the value "C" (hidden from the user on the pasteboard) which then shows records on a portal where the relationship is between the hidden global letter field and the calculated initial letter.
I'd suggest you access some of the excellent resources (Technical Resource Centre tab above) to find out a bit more about relationships. Also look at Kevin Franks resources particularly AnchorBuoys: