SCHIP Extension Act of 2007 - Amends title XXI (State Children's Health Insurance) (SCHIP) of the Social Security Act (SSA) to: (1) extend SCHIP through FY2008 and the first six months of FY2009; (2) provide additional allotments to states to address SCHIP funding shortfalls for the same period of time; and (3) authorize qualifying states to elect to receive the enhanced portion of the SCHIP matching rate for coverage of certain children under SSA title XIX (Medicaid).