There are two things you will have to do:
1) You will have to open create an ininbound firewall rule for ReportingservicesService.exe
2) Rule to Open the port 80
The machine need not part of domain to use the reporting service. I have installed it on my laptop (but that was on xp) and was still able to use it.
I think you should have been able to open reporting service without opening port 80 if you were on the same machine. But may be because you are using the ipaddress instead of the localhost in your url, you might be having port problems
also go reporting service configuration manager and check the urls in "Web service url " and "Report Manager URL"