There are a few 02 Citreon Xsara Picasso advertised on carzone at between 1,400 and 2,000: they'll probably sell for a good deal less than this. Presmably, they probbaly don't have quite the same problems as yours.
Given that, I think you'd be mad to spend anything on it to help sell it, as these prices represent the absolute maximum you could get for it.
I know somene who got around 600 for a similar car when he sold it for scrap last year, so my advice would be to do the same. I'd imagine trying to sell privately would be a lot of time, effort and grief.