Computer advice please. I have an older laptop running windows xp and I need to keep it that way, but it only has a 40gb drive, which is full. I have purchased a compatible 120gb drive.

How do I go about mirroring the 40gb drive onto the new drive, including the operating system and make it the bootable drive? I have an external drive I can use to store the mirror image for transferring the data. (Laptop only holds one drive)