Technical argh

This is starting to really annoy me. My laptop wireless refuses to properly talk to the wireless router. But where the problem is completely beats me. Certain web sites, such as google, work no problem. Other web sites, notably LJ, work for a bit and then resolutely refuse to work for ages, even though the rest of the web is working just fine.

This has me perplexed. Anybody have any pointers as to how to find out what's going wrong?

Edit: will try advice given here