Petrol Engine for Bicyle?

Hi everyone,

I know nothing about Mechanics, but in the smallish city in England
that i live, I think a petrol powerered bicycle would be really cool!
The traffic is always bad here, so I wondered how feasible it would be
to attach an engine to a bike. (I'm not interested in an electric
motor)

Does anyone know of any simple petrol motor kits which are sold that
can be attached to a bike? I found one example of such a bike called
the VeloSolex: http://freespace.virgin.net/stones.ukp/velosolex.htm
but it's nearly £1000.

I found one on Ebay, but it's located in Austrailia, but better priced
at: £282.

Any hints or pointers?