Hello, I hope the following assists you.
This will refer to the front anti roll bar link on the driver's side of the car, the link has a ball joint at each end, this joint wears which tends to result in a slight noise from the suspension as you go over bumps.
Replacing it is pretty straightforward, around about half an hour labour per side and the parts are quite cheap. An example of the part required is http://www.ebay.co.uk/itm/Citroen-Xsara-Picasso-1999-2007-Front-Stabiliser-Anti-Roll-Bar-Drop-Links-x-2-/230916711708?pt=UK_CarsParts_Vehicles_CarParts_SM&fits=Model%3AXsara+Picasso&hash=item35c3b5651c
If you don't replace the part it doesn't make the vehicle dangerous but if left for too long the ball joint on the link can separate from the link.
I hope this answers your question but if I can assists further let me know and I'll reply as soon as I'm able to.