I know Bill Carpenter personally, and I have heard him speak. As others have said, he had a tape about his conversion story called "A Light Shall Break Forth." Amazon.com says it is not available, but it was recorded in 1990 by CFI (Cedar Fort Inc). I don't know if he's in CES now, (apparently not), but I know he was at one time.
I might suggest you get the book "Why I Believe" that Deseret Book published just before the Winter Olympics. It has the testimonies of the most well known Latter-day Saints, many of which are conversion stories (like Gladys Knight's story). Here's the link:
http://www.amazon.com/Why-Believe-Church-Jesus-Christ/dp/1570087237/ref=pd_bbs_sr_2?ie=UTF8&s=books&qid=1210261458&sr=8-2
There was also a book published years ago called "From Clergy to Convert" by Stephen Gibson which is also available for cheap on Amazon.com:
http://www.amazon.com/Clergy-Convert-Stephen-W-Gibson/dp/0884944921/ref=sr_1_1?ie=UTF8&s=books&qid=1210261645&sr=1-1
Also, Elder Hartmon Rector Jr. published a few volumes of a book called "No More Strangers" which is a compilation of conversion stories.
http://www.amazon.com/No-more-strangers-Hartman-Rector/dp/0884943127/ref=sr_1_7?ie=UTF8&s=books&qid=1210261756&sr=1-7
I don't know where you live, but I'll bet the BYU library would have all of these.
Best wishes with your project!