Dear Krishan Gopal,
Computer Networking is a very broad term, which includes Networking of computers with servers, routers and switches, AMC of servers/computers and up-gradation of anti virus definition through net/cloud or through physical medium such as DVD, CDs or pendrives.
You may avail the CENVAT credit on such taxable services provided by the service provider. It is within the scope of phrase 'Computer Networking'.
Please also get clarification from the Commissioner of Service Tax and if possible go for advance ruling if the amount involved in this transaction is substantial.
Regards
Team YAGAY & SUN
(Indirect Tax Consultants)