Are you using an IP address or a computer name to connect?
go to a cmd prompt on the PC you are having trouble with and type in
telnet (your rcc server ip address) 80
like this. telnet 10.0.1.203 80
it should connect and clear the screen (no text). hit the enter key a couple times and see if it spits this out below.
HTTP/1.1 400 Bad Request
Server: Microsoft-IIS/5.1
Date: Tue, 09 Mar 2010 20:13:08 GMT
Content-Type: text/html
Content-Length: 87
<html><head><title>Error</title></head><body>The parameter is incorrect. </body>
</html>
Connection to host lost.
This will tell you if it's network or browser related. If it can't connect, then it's network or firewall related, if you get the above messages, then you are connecting and it is a browser issue.