I had a similar problem with an earlier version of RedHat (I haven't used 7.2). Check /etc/resolv.conf for DNS (ensure same as windows setup.
Also check browser proxy settingd. I didn't have any trouble with a standard firewall setup set to "high" on RH7.1.
You might also check /var/log/messages when you log on - it should bring up DNS information as well as PPP.
If you are unsure as to whether you have a browser or DNS problem, or just a logon problem, see if email works, inwards and outwards. If email is functioning, most likely you have a DNS or proxy setup problem.