PC very slow to establish a network connection on startup.

I have Windows Vista Ultimate running on my home PC with a lan cable directly into my broadband router. Now I must have installed something over the past few weeks to cause a problem, but I'm not sure what, because now it takes several minutes for the machine to establish a network connection.

Is there a cool way of finding out what the culprit is that's slowing down the network connection at startup and deal with it ?

I've run different utilities such as Windows Defender and CCleaner to disable as many as possible programs and services at start up but it still takes ages to establish a network connection.

Thanks.