You are saying there is currently an OS on the 80GB WD which you want to transfer over to that 10GB WD? There will not be an easy way to do it..you cant simply copy all the data over to the drive..it wont boot. You need to capture all the boot sector and all that crap.
So what you could do is use partition magic to partition to repartition your 80GB HD as needed..it will be a tough one though..I need to see what the best approach would be..but I need to know how much space is left on the 80GB HD and how much have you used?
Once its all partitioned right you can use something like norton ghost to simply "clone" the C:\ partition to that 10GB HD and it will boot to that new drive no problem if its in this same PC that is. It wont boot in another PC.