Gurpreet,
ASA5510 is a good firewall. I do not quite understand what someone may mean by "when we create owa or remote access connection it's hit the firewall directlly and not good."
1. You can configure translation for inbound connections (RDC or OWA) and
2. Only allow certain IP addresses on the internet to be able to access it only using specific port (tcp 3389 for rdc and tcp 443 for owa)
-KS