Ah, Ian, I should have mentioned, when I said 'wonderful' I was actually being a little sarcastic.
The Dell does not support a PS2 -> USB adapter (confirmed by Dell themselves)
They even had the cheek to say it was the adapters fault, they found no problem with producing an all USB machine that did not support the adapter. Personally I think it is very poor.
The only one I can find is the Belkin ErgoBoard Pro, which costs about £20 in the USA, but the only place I could find in the UK bounced my order, saying it was dis-continued