I think that, as others have said, you're OK in Holland without mode S if you stay below 1200'. There's anectodal evidence on various fora that ATC may, on request, allow you above this altitude even if you only have mode c. Thge bigger problem with Holland is that it appears the Dutch require you to have a fixed ELT. A PLB is apparantly not an acceptable substitute.
In Germany if you stay below 5000' then you don't need mode s
Having just come back from EDLN on monday, The Avionics people advised me under EASA that ELT will be manditory from 2010 and so is also mode 'S'. Their only comment was Canada already manditory with ballons and other ultralites and gliders exempted. They have been fitting several a month and will fit mine next annual.
The Dutch don't appear to be able to read mode 'S' as they always give me a squawk number or let me continue with a squawk asigned by Brussel info or Langen. As I have said before apart from the Antwerp/Brussels corridor have when I request altitude climb obliged.
Even the French or should I say Calais LFAC have not refused me for not having an ELT. As EASA mandate appears to be 2010.
After all, we are supposed to be JAA EASA for the whole of Europe? Meaning we are all supposed to sing from the same sheet!