First determine the "size" (physical) of the unit. Many from laptops are 2½", but some are 1.8", and a few other sizes possible. Then go looking for enclosures for this drive size. You need to choose one that has an INTERNAL interface for IDE (or PATA) drives of that size, and an EXTERNAL interface (connection to your computer) that matches what port is available on your machine. That may be USB2 (maybe even USB3), eSATA, or IEEE 1394a (aka Firewire 400). Many come with two of these external interfaces, some with three.
Since you're using a smaller laptop drive, you MAY be able to choose whether or not you want an enclosure that comes with its own power supply. Many enclosures with USB2 connections can be used without that - they can get enough power from the USB2 port to run, as long as the HDD you mount inside uses low power. Firewire ports sometimes have power available if you use the right connection cables, but eSATA usually does NOT. Some people prefer to have a power supply module for the enclosure, and others prefer not to bother and like to use just the USB2 connection for both power and data.