I am not sure if this is the way DataSprings would recommend implementing this feature, but it worked well for me. I have a custom profile field named 'Organization'. I set up a search field on Organization using 'Begins With' and a text box.
I then used the following in an HTML module that I placed directly above my DUD module on the same page. Passing the querystring variable with the first letter, and using the AutoSearch=true are the two items that work the magic behind the scenes.
(I changed the opening and closing anchor tags from each line to brackets and changed href to hrf so the text below would display correctly.)
[a]hrf="directory.aspx?Organization=a&AutoSearch=true">A[/a]
[a]hrf="directory.aspx?Organization=b&AutoSearch=true">B[/a]
[a]hrf="directory.aspx?Organization=c&AutoSearch=true">C[/a]
[a]hrf="directory.aspx?Organization=z&AutoSearch=true">Z[/a]
[a]hrf="directory.aspx?Organization=&AutoSearch=true">All[/a]
Works well for our site anyway:
http://www.geneseo.org Hope this helps someone else. It took me a while to figure this out as I couldn't find much documentation on it.