Primary & booster vaccination study to evaluate the immuno,reacto & safety of 3 diff. formulations of GSKBio'combined Haemophilus influenzae typeb-meningococcal serogroups C & Y-conjugate vaccine & one formulation of GSKBio' Haemophilus influenzae typeb-meningococcal serogroup C conjugate vaccine each given concomitantly With Infanrix penta (DTaP-IPV-HepB vaccine), vs Meningitec meningococcal SerogroupC conj.vaccine) given concomitantly With Infanrix hexa (DTaP-IPV-HepB-Hib vaccine) in infants according a 2-3-4 mth schedule