Is this with everything or just with browsing the Internet?
I ask this because Linux supports IPv6 and new versions like Mozilla 1.6 up also supports IPv6 if your (A)DSL connection hardware doesn't support IPv6 you get problems.
I had this problem also, not that my hardware doesn't support IPv6, in my cases my Internet provider has problems with IPv6.
The fix is to turn-off the IPv6 addressing.
and add the lines;
#Turn off IPv6
alias net-pf-10 off
alias ipv6 off