HOW CAN I RESET MY IPHONE 3G TO FACTORY SETTINGS WITHOUT DELETING EVERYTHING OFF IT?

I only got an iphone 3g and I got so vehement which i filled it with loads of applications and songs (about $30 worth). The alternative day when i plugged my iphone in to the mechanism on itunes it pronounced to reset the iphone to bureau settings. I dont wish to lax all my apps so what can i do? PLEASE REPLY A.S.A.P.