The easiest way, is to just put the new drive in the slave position. Otherwise, you're looking at reinstalling the operating system, or hoping some sort of disk imaging program will work properly, which you'll probably have to go out and buy I might add.
My PC came with a 60 Gb HD. I'd like to add a second HD in the open, available drive space, but I was also thinking of changing the original to a much larger drive.
How do I do this? Move everything from the original drive onto the new one, then install a replacement drive where the original resided?