I would say it could be extremely easy to accomplished if you replace your 2800 router with a Cisco ASA firewall. But that was not what you asking. AFAIK, established option in cisco router ios could only apply to tcp connections so udp and icmp are still permitted even your configuration works.
to verify if established option works you could try to deny your telnet/ssh/remote desktop into your cisco device or windows server/pc in another subnet:
ip access-list extended TEST_EST
deny tcp host YOUR_CISCO_DEVICE host YOUR_PC eq 23 established
#deny TCP establishment between test device and your pc. change 23 to different port numbers if you want to try with other protocol. 80 for web, 3389 for remote desktop
permit ip any any
permit icmp any any
#this two lines are used so that end user will not be disconnected from network
then apply this access-list to the subinterface where target device locates