Hi Siddhartha,
they have number of ways to create custom field in search view but effective way is AET field.
http://scn.sap.com/community/crm/blog/2009/07/14/crm-70-how-to--4-adding-custom-fields-with-the-
new-application-enhancement-tool-aet
go through this links you will get some idea how to do..
How to enhance the standard search with custom field?
Enhancement of search view with a custom field
Search Result Enhancement with custom z fields
Thanks & Regards,
Srinivas.