What materials do I use for a styrofoam background ?

Hello,

After seeing NetMax's excellent response in the thread "What do I use to 
stick rocks together ?" (see Message-ID: 
<[EMAIL PROTECTED]>) I have become convinced 
of the idea of using styrofoam to build a fake rock background for my 
new tank.

Trouble is, most of the pages that showed construction were 
Scandinavian, and I not 100% sure how all of the materials translate 
into things available in the UK (or US for that matter). So, can anyone 
enlighten me as to the best materials to use, and what sort of place I 
would look for them ?

I saw some mention that styrofoam is better than expanded polystyrene as 
it is stronger. This confused me as I thought the former was just the US 
name for the latter !! Anyone any idea what styrofoam is, and where I 
might get it in the UK ?

Also, what about paints, dyes, epoxies, and all the other stuff used ? 
Any information would be greatly appreciated.

TIA

--
Alan Silver