A previous thread may help :

http://groups.google.co.uk/group/alt.autos.peugeot/browse_thread/thread/7db271fa
8887d92c/b892733fe0a8280b?lnk=st&q=206+stereo+speed&rnum=1&hl=en#b892733fe0a8280
b

If it's a later model you may need a canbus interface:

http://www.sailesmarketing.com/searchdetails.asp?ID=50

Failing that you could use a magnet/sensor kit to read the rpm on an
inner half shaft coupling.

And finally (this is not a joke) there was a kit available (Alpine?)
which involved a sensor mounted on a rear wheel arch and a magnetic
"wand" used to magnetise the steel in the corresponding tyre. You may
find a dealer who never got round to binning them all .

J