How to stop a dhcp server from assigning my ip to another computer My system has been assigned an IP that I liked from a dhcp server.  

I have manually given that IP address to my system. Now I am frequently getting an error that someone else has taken my IP address. So my questions are:


While I am using that IP, how this IP can assigned to someone else?
Note: this happens only when I use this IP on my macbook. This never happens when I use my windows pc.
How can I assign an IP address to my system so that nobody else can take that IP from the dhcp server?


It's very irritating when I am in the middle of a browsing session and suddenly an error pops up that somebody else has taken my IP

e.g.

case 1:
I have two systems. system A(macbook pro) and system B (windows pc).
I have given x:x:x:x ip address to system A and now I am giving same ip to system B. system A macbook pro will give error that your ip has taken.

case 2: I have two systems system A (windows pc) and system B (another windows pc). I have given x:x:x:x ip address to system A and now I am giving the same ip address to system B. Now system B will give error ip conflict. I think this is more appropriate error. 

I want the same thing for case 1.
You might want to check out your routers web interface. Usually you can assign a preferred (or probably obligatory) IP-Address to a  specific Mac Address in this case the mac adress of your Laptop. (you might want to read the wikipedia article about mac adresses as it explains a lot more and might be available in your native language)