connect iphone 3G to two computers

[cyclopopcicle]

i need to sync to two different PCs one a laptop the other a desktop
how can i get it to sync to whichever it is connected to, to update from it?
it will sync to the laptop no problem, it will conenct to the desktop but will not sync.

cheers for any help

 

[cyclopopcicle]

ok so how do i set it up to sync with my desktop, as its synced to the laptop at the moment,so its more of a manual thing?

cheers