If you want to "upgrade" a computer with a HDD to using a smaller disk, usually a SSD, you will need to come up with a way to shrink your windows partition. There are some for-pay software packages which do this for you, but no OSS tool which will do it with a simple click. There's a slightly meandering sequence of steps necessary to get everything working correctly. Your best allies are the gparted livecd, and a USB to SATA (probably) adapter to let you hook both disks up to your system at once. This process should work for basically any version of Windows from 2000 on, but I used it specifically with Windows 7.