Generally, salary hike depends upon your experience, qualification & also company standards(in which u r going for interview).
If the Co. is much big then ur current one, u can easily ask for atleast 30-40% hike which is standard for a job change.
Also sometime there standards set by giant cos. such as Tatas & other where u get the fixed salary decided for the particular post or designation.
In this case let the difference be any but ur are entitled to get same defined by the standards of the co.
Hope u have got some clarity in this regards
Best of Luck
15th February 2008 From India , Pune