It seems the system was disconiuned by Citroen as on their website they offer only personal support for unlisted models.
[Please Register or Login to download file] - might be worth asking them whether ther are still updates or maybe if the software can be updated.
Last "hope" would be Ebay and the replacement of the whole system with a CE in dash unit.
But again for the Xsara Picasso not the easiest task.
Update:
Found a working Link (thanks to Meisterjäger) for something called "
CITROEN / PEUGEOT - Update-CD 8.20 - RT4 / RT5"
[Please Register or Login to download file] Burn with ISOBURN at 4X or use a USB stick if the device is unlocked.
No idea about the unlock or if the file is for that system, I only found it and offer the same instructions as in the original posting.