I had the option of the Corsa as a company car, but none of the dealers near me had the model I wanted to test drive, so I went for the fiesta. When I have had a poke about in them, the interior does feel netters made than that in the fiesta although not as design flair (its quite germanic in its approach). One thing that I did prefer was the 6 speed box in the derv engines I was looking at, which would be better on a motorway.
If the SRI derv had been on the list, I think I could have been persuaded; EVO gave it a pretty good review a few months ago. Although, if I had my way, I would have had a Mito or DS over both the Corsa and Fiesta.
My other half bought her Corsa (shape before yours) on the same deal, no deposit, no interest and a year free insurance. Although not a drivers car, it has been so reliable over the last 6 years and is cheap to service. It was certainly more reliable than my beemer which had a list price almost three times more than the Corsa.
Good luck with it, hope it turns out to be a good purchase.