Vaclav,

It sounds to me like it's more of an issue with your internet service provider than your computer, especially if you get the same result in IE and Firefox.

Quite often ISPs don't put enough resources into the server providing name to IP address resolution for their customers.

If you're comfortable changing network settings, then I suggest you either use Gibson Research's DNS benchmark (http://www.grc.com/dns/benchmark.htm) to find one that will work better and respond quickly, or change it to 8.8.8.8 which is Google's public DNS (Google provides instructions at http://code.google.com/speed/public-dns/docs/using.html).

It's changable on your PC, or on your network router but the Google instructions should get your through it in either case.

Good Luck

--B3