Iain,
The Pixcel 255 is a rebadged SBIG ST-5C. You can download the free CCDOpps and run it from there. Easy peasy.
Here is a page you've probably seen already:
http://www.company7.com/celestron/products/pix255.html
There are other pages with info and example pics around, just search for ST-5C.
Cheers,
Jason.