Ok mate, Basic Tuturial for ya

Firstly dont bother with any kind of expencie painting kit, Just buy a tin on calaper paint from halfords, No need for an undercoat what so ever, One tin gives you enagh to pain the calapers of 50 cars. Also, buy some alloys cleaner too.
Remove the wheel, spray on the alloy cleaner onto the calaper, Then leave it to take effect for about 5 minites. Then, Using a wire brush or some kind of abrasive surface (i used wet and dry) scratch off the surface rust as best as you can, Giving the surface a quick wash every 2-3 mins untill the calaper is a sorta black colour with some spots of rush (doesnt need to be perfect)
Now you can tape off th calapers etc if you like, However if like me you have a steady hand with a paint brush, just paint the front of the calaper, the top and the side, no need to do the back, no ones going to see that area are they?
Apply 3-4 layors of paint at intervals instructed on the tin, (the pain should only cost ?4.99) then leave to set. It should be drivable withing 3-4 hours

Here is how mine came out:
