For information about the ISEB Manager's Certificate in IT Service management, please see this Web site. You'll also want to read the guidelines at this site.
As far as I can tell, this is a professional development effort that combines training and exams to advance already-certified managers -- who must first obtain an ISEB/EXIN Foundation Certificate in IT Service Management (or the ISEB Network Service Management Certificate, which gives exemption) -- into more senior certifications in the specific areas of service support or service delivery.
As far as ITIL goes, that refers to the IT Infrastructure Library, a largely European approach to managing IT services, supported by British Standard 15000 (BS15000). See this Web site for more information.
It sounds like you're considering employment somewhere in the European Union, if not in the UK. Good luck and hope that helps!
This was first published in September 2003