Yeah a ssimple Karcher pressure washer would suffice, I run one using a foam lance and PH Neutral Snow Foam from the website below (in fact the 350Z pictured is mine, to give you an idea of the thickness).
http://www.cleanyourcar.co.uk/washing-and-drying/foam-lance-various-fittings/prod_371.html
Here's the method you should use:
1. Jet down with water first to wet the car, remove dirt / dust / debris from body, under arches etc.
2. Bang the foam lance on, 1cm of foam solution and filled to the top with warm water, completely cover the car and allow to soak for 5 mins.
3. Thoroughly rinse
4. I then fully foam it again, but with some shampoo also in the solution, and then proceed to wash from top to bottom with a microfibre wash mit (using a two bucket method i.e. one bucket with your suds in and one for rinsing your mit (to get rid of any grit it picks up).
5. Rinse down fully.
6. Wash the wheels
7. Dry the car using terry towels / microfibres and buff up
... then go on to do whatever polishing you're doing (if) and Robert's your mothers brother
I found it halved the time of my usual routine. I also used the foamer to do all my house windows & doors too, it's bloody good fun and addictive
Hope that helps!