I think the web proxies prevent the web server from gathering your IP address, and can't do anything to hide your activities from your ISP. What would do it was if you were connecting through a large anonymous network (for example a school network). This just means that the ISP sees one IP address accessing http://www.blah.com and the same IP for http://www.schoolhomeworksite.org. This means it's a bit harder for your ISP to pin something down to you.

However, getting connected to a large network could be a bit of a problem for home browsing...

One last thing Barov4e, it is impossible for you to manually change your IP address that your ISP uses, otherwise you could steal someone else's address, and pretend to be them, you can however change it for your network. But, you can't change your MAC address, as this is hardwired into your network card.