Your ISP is your internet service provider Who do you pay for internet access?
If it's Clearwire, they're probably your problem... they do block p2p. There's a little info here
http://www.irishisptest.com/forum/ar...php/t-104.html

If you're using the Norton firewall, make sure XP's firewall is off... the 2 won't work together. Does your modem have a model number?

If Clearwire is your ISP, you could try changing ports. No guarantees, they might monitor different ports & block you wherever. There's some info here
Alternative Ports