Depending on the type of mortgage you plan to take out or are eligible for, down payments for certain types of loans can range from 5%-20% of the purchase price.
Take action to improve your situation if a low credit score if making it diffucult for you to get a loan. You may check out improving your credit score on MyFico.com. which is most often used by lenders to gauge your risk level. There may be a small fee to get your actural credit score.
There are other websites that can help you check your credit score. Visit annualcreditreport.com for a free annual credit report from each of the major reporting agencies.