How small is it? in GB. I only ask as laptop drives have smaller hard drives than desktops. 80GB is the maximum freely available.
It is possible but you'd actually need to buy a new hard disk drive and have it installed as a replacement for your current drive.
Have you considered adding an external hard drive? If your laptop is fairly modern(1-2years old) it should have a USB2 or FireWire port which would make this an attractive proposition but would require a separate power source possibly cutting down your portability.