can any body tell me the difference in RA's of ACAS and TCAS observed by the flight crew>?

There is a great deal of information on the evolution of ACAS on the web, try a google search. The Eurocontrol TCAS/ACAS site is a good place to start your research.
EUROCONTROL - Frequently Asked Questions (FAQ) (http://www.eurocontrol.int/msa/public/faq/ACAS_FAQ.html#qa10)

ACAS Principles are outlined in their FAQs

What is the difference between TCAS and ACAS?

TCAS (Traffic Alert and Collision Avoidance System) is a specific implementation of the ACAS (Airborne Collision voidance System) concept. TCAS II version 7.0 and 7.1 are currently the only available equipment that is fully compliant with the ACAS II Standards and Recommended Practices (SARPs).

ACAS II provides "Resolution Advisories" (RA's) in the vertical sense (direction) telling the pilot how to regulate or adjust his vertical speed so as to avoid a collision.

TCAS II Minimum Operational Performance Specification (MOPS) have been published by RTCA (DO-185B) and EUROCAE (ED-143).

Thanks happy biker. You were really helpful. i got all the details and completely understood all the differences...
happy landings