Mr. Laskar, 1st of all note that there is no such thing as a SMALL DEDUCTOR. A proper categorisation would rather be (1) Deductors who are covered under Tax Audit u/s. 44AB and (2) Deductors to whom Sec 44AB is not applicable.
Regarding online payment of TDS, the following persons are MANDATORILY required to pay taxes ONLINE :
(1) Corporate assessees
(2) Persons required to get their accounts audited under sec 44AB.
Other than these persons mentioned above, there is no compulsion to pay taxes online.
HOWEVER, there is a recent ammendment made to this rule. According to CBDT Circular dated 25th March 2009, WITH EFFECT FROM 1st April 2009, all tax payers will be required to pay taxes online, irrespective of their status. In case of TDS deducted on or before 31st March 2009, old method of payment of TDS is valid even if it is paid in April 2009 or later. BUT for TDS deducted from 1st April 2009 onwards, compulsory E payment is to be made.
The Challan form for the same is also changed. Now a new Form No. 17 will be applicable instead of the old Form No. 281.