Small Business Private Investment Act of 1979 - Amends the Internal Revenue Code to allow a credit against the individual income tax for incentive stock (original issue common or preferred stock) acquired in a domestic corporation whose equity capital does not exceed $25,000,000 immediately before the unrestricted public offering of such stock. Specifies the amount of such credit to be an amount equal to the sum of: (1) ten percent of the first $10,000 of such taxpayer's adjusted basis; plus (2) five percent of any other amount of such adjusted basis. Limits such credit to $3,000 annually ($6,000 in the case of a married individual filing a joint return).