Hi Srinivas,
The way to configure the logon page in the portal is different between EP 7.0 and EP 7.3.
Please have a look at SAP Knowledge Base Article:
1935486 - NetWeaver Portal 7.3X/7.4 and custom logon screens
It contains references to the formal documentation of the portal on how to configure the logon screen, or develop a custom logon screen, in the new version.
Hope this information helps,
Thanks & regards,
Michal Zilcha-Lang