I'm no expert myself but I'm willing to try to help. From what you say you can connect to your ISP via pppd. However you get errors to the effect that it cannot recognise (it really means find) the addresses you enter in the web browser. This is DNS lookup error (Domain Name Service). When you enter a web address it has to go find the IP number for that address (e.g 220.127.116.11). It does this by querying special DNS computers on the net, but it has to know where to find them. They are normally computers on your ISP network. When you connect via pppd entries should be added to the file '/etc/resolve.conf'. Take a look at this file before and after you connect to the net and see that new entries for 'nameserver' get added. Also see if you have an entry of 'nameserver 0.0.0.0', if not add it, it means DNS servers are to be found on the default gateway.
Hope that helps some, BashTin.