Help web page not available - browsing on wifi


i've been having some issues lately with browsing websites on my desire, when connected to my home router. this has started to happen (i think) about a week ago, after i have changed my isp.
the simptoms are: i'm hitting the search key and searching for something. then the browser opens with the google search results. i then click on a result page and wait for it to load. and wait, and wait and wait, and after some more waiting it times out and says 'web page not available'.
some websites do work every time, with every request, some only work sometimes or maybe today they do and tomorrow they don't.
usually after i clear the cache, cookies and stuff, it seems to work for a while at least.
this is happening with the stock browser and also with dolphin browser hd and only when i'm connected to my home wifi network.
the new isp connection (which i suspect to be the culprit) is a pppoe connection rather than a lan connection (which i used to have). this may not have anything to do with it but just wondering...
has anyone ever had or heard of similar issues?