Updating Iphone 4 After Backup?

So,The New IOS 5 Is Out....I am thinking too update my iphone 4 to ios 5.....4.3.5-Ios 5....So If i update my iphone will all my stff be gone....Like...When i plug in my iphone it says Will you like to update your iphone to IOS 5. I Was Thinkign To Backup.But I DOnt knwo....I Have all My STUFF in my iphone in another computer and the other computer is broken.So If i backup the iphone and then update...If i backup my iphone,and THEN update..Will my stuff on the iphone still be there or will it be gone....Please Reply As Soon As Possible.REMEMBER: the computer i synced with my iphone 4 is broken. so i dont have all the music,photos,movies that my iphone has right now