OK, I pulled the headunit out, and this is what it said :

Blaupunkt Alfa 937 CD Mp3
7 643 392 316 e1 022330

I don't know if this is of any use to anybody. I'll write an email now to PIE and see if they can help me.
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Riocar 80gig S/N : 010101580 red
Riocar 80gig (010102106) - backup