Hi i found this in a mac board and its very usefull

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For those of you who know me well, you know that have I bandwith like no other. In order to achieve this bandwith superiority I did this: 

-open the Terminal and type "sudo -s" to access root  

-type "sysctl -w net.inet.tcp.recvspace=65536" then press enter (increases recieve buffer size)  

-type "sysctl -w net.inet.tcp.sendspace=65536" then enter (increase send buffer size)  

- type "sysctl -w net.inet.tcp.delayed_ack=0" then enter (increase your Mac's response time)  

-type "logout" then enter (if its a login shell)  

This hack only works for the current boot up (it will be gone next time you start up) so let's fix that:  

-type "sudo pico /etc/rc"  

find the last line that should read "exit 0"  
NOTE: The "exit 0" line is the very last line in the text. You need to hold the down arrow key in order to reach this line.  
since we want the effect to take place during all boot ups,  

-type the 3 sysctl commands again right above the "exit 0" line, writing one per line  


Results will vary, people's bandwidth has doubled because of this. Others have seen no noticeable difference. It sure helped me and I hope it give your Mac a nice speed boost too!
after that an addition from zodiac for people who uses leopard



Code:
using command line in terminal just working fine but how to make it lunch every time the system boot since there's no /etc/rc in leopard ! 

Well, there's little app called Lingon will do the trick. 
Link: http://lingon.sourceforge.net/  




	

		

			

			
				Lunch the app click New, choose Users Daemons.
1st box is the name "Type whatever you want"
2nd box is where you will place the command "sysctl -w net.inet.tcp.delayed_ack=0"
Finally you need to check that second option in third place "Run it when it is loaded by the system (at startup or login), Save, reboot and its done !
			
		

	



Another way >>
Link: http://rapidshare.com/files/75905454/0_Net_Delay.plist.html



	

		

			

			
				Place this file in this folder /Library/LaunchDaemons 
fix permissions "sudo chown -R 0:0 /Library/LaunchDaemons/0_Net_Delay.plist"
			
		

	



Notice: this file is only for net delay as long as no need for increasing recieve/send buffer size coz its already done in leopard at least at mine. if someone needs to add this 2 commands just let me know. 

To be sure that you have done it next time you boot open terminal type > "sudo sysctl -w net.inet.tcp.delayed_ack=0" 
if you get this line "net.inet.tcp.delayed_ack: 0 -> 0" that mean its working if you get 3 -> 0 that mean you have done something wrong.