Hi,
I m a newby in linux. when browsing from Windows i can access all the sites, but in linux some sites are not reachable all the time(they r sometimes accessible,though).
i can get the ip address by using nslookup, then i tried to browse by copying that ip address, but browser cant find the sites.

what may be the problem?

The only times I've seen this it was either DNS or the interface MTU setting on an ADSL connection. Since it works for you with windows, it's probably not DNS. Do you have an ADSL connection to the internet? It may be worth booting into windows, running ipconfig /all to get the interface settings and confirming that they are like the settings shown by ifconfig under Linux.

When i failed to get www.orkut.com, then i typed http://orkut.com and it got to orkut, i thought that was a fluke, but since then when i have that kind of problem, i tried and got access

Have you looked at the contents of the /etc/resolv.conf file? Often times the file will have the name of the home network at the top followed by a list of nameserver ip addresses. Maybe even just the network name.

I always found it more reliable to not search the network at all. You can use ipconfig /all from Windows to get the addresses of the DNS servers, then in Linux edit /etc/resolv.conf to have just those lines, like this:

before:
search NETWORK
nameserver xxx.xxx.xxx.xxx
nameserver xxx.xxx.xxx.xxx

Get DNS server addresses from Windows

after:
nameserver xxx.xxx.xxx.xxx
nameserver xxx.xxx.xxx.xxx

If you are using a Mozilla browser like Firefox/Seamonkey:

The problem may be with IPv6 ("Internet Protocol version 6"). To disable IPv6, change the preference network.dns.disableIPv6 from "false" to "true" . Here are the steps:

1. Type about:config in the address bar, press Enter.
2. Find network.dns.disableIPv6 in the list.
3. Right-click -> Toggle.
4. Restart Firefox/Mozilla Suite and try again.

If this doesn't work, re-enable IPv6 by resetting the preference to "false".