Busted/Rounded Screw, how do I unscrew it? :/

Hi,

Ive successfully changed the glass,lcd and digitalizer on my iphone 4.

But when I was going to unscrew the dock connector to exchange that aswell I ended up rounding the screw so that now the screwdriver doesnt have any grip inside the screw.

Does anyone have a good solution for this problem?

Thank you for your help.

/Bo