A Q plate used to stand for 'query', meaning unknown date of origin. If you have one of these you cannot put a personal plate on the car.
If you have a new (e.g. 57) registration, then you can put any private plate you like on the car as long as, as Craig says, it doesn't make the car appear younget (e.g an 08 reg).
Legally, the style of the plates are now governed by law, and supposedly controlled by the plate makers, who should ask for proof of ID andthe log book. However, many companies make 'show' plates, which you can order over the phone without any of that. These are not meant for road use and could potentially fail an MoT. I've got show plates on my Audi and its passed its last 4 MoTs with them on, so go figure.
As for black and white plates, these are only meant to be fitted to pre 73 cars, and if you were to fit black backed plates on a modern car you'll likely get pulled, but on a classic (or a car that looks like a classic) its unlikely.
Finally, stick on plates are meant to be illegal too, but I think the real problem is the angle at which they are presented so as to be clearly read. I have a stick on plate on the front of my Caterham and it always passes (well, it did until now anyway...)
Hope that helps
