Many thanks for the people that put this all together.
I bought a Fujitsu 80GB (MHT2080AH) from
www.lowestonweb.com for £60.59 ex VAT (£71.19)and I was really please to find that when I opened up my DMS, there was a virtually indentical Fujitsu disk in it. This meant the swap was as easy as could be.
I did the CD Image upgrade and everything worked as it should...until I put the new 80Gb DMS into the hacked Phatbox and it said "No Magazine" on my Audi headunit.
I then followed the instructions
HERE and it solved the problem. (Thanks Genesis!)
I went very slow and carefully through the process and it was all complete inside 1.5 hours. I could have done it a lot quicker but I reckoned slow and methodical was the best approach.
Oh I forgot to mention - I bought a VW Phatbox to go into my Audi as it was cheaper and I already had the cable as I had a OEM 6CD player already in there.
I removed the case so it fitted in the OEM 6CD position in the glovebox.
Many thanks again. I now have a 80Gb Phatbox for a grand total of £240. I'll certainly be making a contribution to this site.