Can anyone tell me how I transport a head off one person onto a picture of another

this will help

I think I have training needs, come on you clever twit, hwo did you do that

I'm no expert, but you'll need something with a bit of oomph to get anything that looks even halfway convincing. A basic package that comes with a Camera is probably not enough - beyond a bit of redeye reduction and general touching up (ooer) they're not really designed for it. You need something a bit more arty - Adobe Photoshop is the market leader but expensive, there's a cut down version called Photoshop Elements that's about 50-60 quid I think. PaintShop Pro is about the same price. Failing that there's a free package called The Gimp which is very powerful but takes a bit of persistence to learn and use.

Essentially you'll be looking for something that will identify edges and allow you to automatically cut based on them (Edge Detect Tool?), or something that will allow you to manually put an outline round an irregular shape and copy it. Then you can paste it across. To make it look really convincing though you'd probably have to spend quite a bit of time using the airbrush on the join to try and blend things in. If it's a joke for a mate you can probably get away without doing that.