The cpu's, hdd, dvd's etc should all be pretty universal, but Dell motherboards do tend to be a little different to the norm.
To find a cooler, you'd have to find out what socket type your cpu is, then take off your cooler and measure the hole centers in the motherboard to see if they match up with 'normal' boards.
A good cheap cooler like an Arctic freezer pro is about £20, up-to £60 for a very good cooler, then your going into the £100's for water.
If your going to spend more than £100, you might as well buy a new CPU and motherboard. (much more performance than cooling yours down)