Sagnik,
I also noticed that you are using the other OpenACS RPM's. Even tho you uninstall all the postgresql rpms at once (as mentioned in my previous response), it would not work because there will still be failed dependencies on the pgdriver, aolserver and openacs rpm's. If you REALLY want to uninstall postgresql in this case, you will have to reverse the sequence that you have the rpm's installed and uninstall them one by one.
Also, after reading thru other threads you posted, I assume you are trying to upgrade the postgresql from 6.x to 7.0x. For your information, RPM has an option of -U, which does upgrading. But then, if you are running 6.x now, you will have to reload the data model for 7.0x. So what you should do now is to remove all OpenACS-related RPM's in reverse order and then reinstall everything with the new Postgresql version RPM.
Again, please read the documentations and not just use the RPM for "ease", you would lose the chance to learn some fundamental knowledge about setting up OpenACS.
Sincerely,
