It IS possible to get the hard drive out of a laptop. But the laptop might not be a lot of use later! You can get cases for 2.5 inch drives.
3.5 inch drives is easy. Lots of choice of external housings, many will connect via a network cable or USB2 cable.
So if you can get the hard drive out it's easy to keep it on the shelf in a case to retrieve data from.
If you can't get the old laptop drive out, you can probably make an image of it on an external drive by using Drive Image or Ghost, and then you still have the backup you can use as a slave on the new machine.