3GS- lost backup file, how can I create a new backup file

My computer crashed and I dont have a way to get the original backup file. I have a new computer and I need to create a backup since I am replacing my 3GS with another 3GS tomorrow.
How can I do this? I dont want to loose the pics, MMS, SMS or contacts.
I saw another thread but the thread is about retrieving the old backup file from an old computer. In this case I dont have the old backup file, I need to find a way to create a new one if possible. Please help.