>Sorry for the misunderstanding. What I ment was to go into the device manager->ports->communication port (com1) and go to properties. Then under the port settings tab -> advanced you can change the com port number. This will mean that the computer will no longer have a com1.
>

Your suggestion solve my problem, Thanks you!

BTW, just wonder why it happen on WinXP only, why the com port 1 is being occupied when the PC just boot up?? is it the WinXP behaviour or bug?? I try it on 4 WinXP PC, there are 1 with WinXP SP1, 3 with WinXP SP2, only one of the PC with WinXP SP2 which got 2 com port (com 1 & com 2) work fine on both of the port, others all need to use your suggestion to solve the problem!!