Some lender will go down to 620 but the price will be adjusted. 640 and better is really where you want to be. This will get you a reasonable interest rate. This is just a starting point. There is more that goes into a loan such as debt to income and loan to value. Please feel free to contact me for any questions that you have.
As a lender I may know of different programs and the qualifications for them. If you have a realtor and a lender that can work together we would be able to find you a house and program that would work for your situation. Feel free to contact me thru here if you have any other questions for a lender.
Both Cheryl and Rita have some good advice. Depending on the degree of the disability there may be programs or at least a way to lower your taxes. Some of it will depend on where you are looking to purchase. Speak to a lender also to see what programs are in place.