Comparison of GSK Biologicals' DTaP-IPV Candidate Vaccine to DTaP and IPV Separately Administered Vaccines in Terms of Immune Response and Safety

Inclusion Criteria: * Healthy children between and including 4 and 6 years of age. * Previously received 4 doses of GSK Biologicals' DTaP, 3 doses of IPV vaccine and 1 dose of measles, mumps, and rubella vaccine. Exclusion Criteria: * Use of any investigational or non-registered drug or vaccine other than the study vaccines within 30 days preceding the administration of study vaccines, or planned use during the study period. * Chronic administration or planned administration of immunosuppressants or other immune modifying drugs within six months prior to study vaccination or planned administration during the study period * Administration of immunoglobulins and/or blood products within 3 months prior to vaccination.