You are required to apply to a specific home ownership program in order to have your section 8 voucher apply towards a mortgage. It is not a quick process and there are limitations. Check with the housing authority you are tied to for more information.
Broker Baird & Warner
http://www.thecha.org/pages/mobility_counseling/2639.phpThe Mobility Counseling Program assists families in the Housing Choice Voucher (HCV) program to move into CHA designated Opportunity Areas within the City .
Geof and Bill are on top of it. Before talking to a lender I would work with CHA to see what steps you need to take with them first. Remember that even in these programs you will have have a credit score of at least 620. I would personally start with the CHA than I would check my credit and I there is a problem, start to fix my credit to make sure I had at least the minimum credit score of 620.