Run a trace route through command prompt to various IP's and see if there's any differentiation. If not, your ISP is fucking up, probably having DNS resolution errors.
My advice to fix your high ping would be to connect your modem to a sweet router.
I recommend the Netgear Rangemax WPN824 v2 or the D-Link DIR-625 /smile.gif" style="vertical-align:middle" emoid=":)" border="0" alt="smile.gif" />
I put in the WPN824 v2 and it created a huge boost in speed across the home network and its not too expensive /wink.gif" style="vertical-align:middle" emoid=";)" border="0" alt="wink.gif" />
linksys router rule i never had a issues with them /smile.gif" style="vertical-align:middle" emoid=":)" border="0" alt="smile.gif" />
and root has a good point make sure it locked down teh wireless... /tongue.gif" style="vertical-align:middle" emoid=":P" border="0" alt="tongue.gif" /> if your useing that lol