I frequently get asked aobut gifting money for a down payment to help out a child. Giving your child a gift of cash for the down payment on a home works like this. Currently, you can give up to $12,000 a year to an individual ($24,000 through gift-splitting with your spouse) and not have any gift-tax impact. So you and your spouse could give give your adult child and his or her spouse up to $48,000 for a down payment in 2008.
Please do talk with your financial advisor prior to any gifting of money but these are the limits.