I currently use just a pressure washer and mitt, but when I replaced a old pressure washer with attachment with soap bottle on the lance I made the mistake of buying one which you put the soap in the pressure washer itself and have to lower the pressure to get the soap to pick up... To say its hit and miss is an understatment Grrrrrrr

AnyWho... I was told by somebody I work with, its not a great idea to snow foam to regularly as it may be harmfull to the paintwork f used say once a week?! Opinions on that?

No more or less harmful than washing your car once a week with car shampoo. Did they say harmful chemically (99% of foaming shampoos are ph neutral and wont strip the wax/sealant from the paint) or just physically due to shooting dense foam at the car? It's all in the technique if that's what they were was suggesting.

When possible mine gets snow foamed every weekend and I know many people who do the same and I've never heard of it being damaging 

got a new karcher yesterday and from my old one I have a soap bottle, which I added some car shampoo too, it didn't really snow, but Rory did get covered nicely and came up super clean after a month of winter slush!

now, what stuff do I need to get a good foam?

Dan i use the Autobrite snowfoam lance and autosmart snowfoam. Puts it on like cloted cream and you can adjust the thickness.


Kevo

if I have my karcher and soap bottle, surely I just put liquid in and away I go?

http://www.cleanyourcar.co.uk/washing-and-drying/gilmour-foamaster-ii/prod_329.html

This is what i have been borrowing, not super foamy like Kev's, but shifts the muck nicely.

The Gilmour can be used attached to a normal hose pipe or pressure washer.

I am more than likely to get the Autobrite or similar for my Karcher though

The best thing about the Autobrite lance is that you can adjust the mix for thickness of snow foam
I know what you about the pictures on the link, that is on a very light setting, if i turn mine up to full its like putting clotted
cream on the car, this is good in the winter as it gives a better dwell time on the car and so lifts the dirt better.
The Autobrite lance is around 50 quid though so puts alot of people off, but its a quality product.
Other attachments do work too
What i do now is spray the car with g101, this is like a pre wash, the stuff you see them use at the handjob places, or similar anyway this shifts all the heavy dirt, then use the foam after that.


kEVO

looking at it, my soap bottle looks very similar and looking at the pics on the linky thats exactly how rory looked yesterday with just putting in normal car shampoo, so if I get a bottle of super foamy stuff I should be getting the same results.

I actually used Turtle Ice, and now Rory feels like I have cleaned him with baby oil  

If you're buying a foaming agent I highly recommend Meguiars Hyper Wash, lasts forever and foams really well (Non-toxic as well if your're environmentally minded)

Here it is in action on my brother's Bravo