I have already installed PostGIS along with OpenGeo suite and it is the latest version. Now I want to run pgrouting but the latest stable version is not compatible to the latest PostgreSQL versions. 

Can I downgrade the PostgreSQL from 9.2 to 8.3?

I can't try some unstable versions of pgrouting that are compatible with PostgreSQL 9.1/9.2 because, there are issues in shooting star algorithm... or can I install another version parallel to this?

I tried uninstalling OpenGeo suite completely and installed only PostgreSQL 8.3 and PostGIS 1.4 but there are more and more errors I am getting and I am afraid to solve those as it's for my mini project and I have only 3 days to prepare documentation...

So someone please help! I am trying but I am confused with these kind of installations.