Variable Access to Websites Via Broadband

[spiderlaw]

I have an ibook G4 running Mac osX v10.4, I have just signed up to a new broadband service provider - i havent had any problems with internet connections in the past but i immediately could only navigate to certain sites - i cannot get to google or my university website (www.inf.ed.ac.uk) and lots of others. I cannot log on to msn messenger but can navigate to some selected sites such as www.apple.com, www.bbc.co.uk etc. i have fought it out with the isp and they insist that it is not their service - i have a valid ip address and they cannot detect any problems with my connection - they did allow me to set up a proxy to their server - this corrects everything except msn messenger (and also seems to interfere with my ability to set up a vpn to my university) I really need these to work! I thought it might be the dns servers - but i have entered these into the network settings and have also tried navgating to the ip addresses i cannot get to and this still dosen't work. if i am going to insist it is the isp and not my mac i need to tell them exactly what it is because they are morons! Please help!