How to change the Internet Protocol Address of Local area connection?

I am using IBM R51 Laptop.When I try to change Internet Protocol Address of Local area connection to use my office Net service,It automatically reverts back to the original Internet Protocol Address.How to avoid the new Internet Protocol Address from automaticallychanging back?

When you try to change the IP, because of your already configured gateway IP, it reverts back to original IP.
So you must first enter a valid gateway IP and then you can easily assign an IP available for that gateway.

Check whether you have any static ip address. if possible release and renew the ip address then it will work..............

do a right click on my network places go to properties of tcp/ip and change that from there manually ...

if u are using a modem then the ip address would be assigned by the modem and if you are using a router then the ip address would be assigned by the router.
If you face problem with the IE then you can try resetting the IE by entering internet options and then clicking on advaned tab and then clicking on reset button.
If you see that your ip address is 169.254.x.x then you will know that this is not a valid ip address and you have to follow certain steps for that:
do a power cycle of the modem.............then release and renew the ip address at the command prompt.
there are more steps depending on the situation......the best way to get resolution is to go to microsoft website and do a research.