I have a Roadcom RC400C Navigation. This works with Windows Core 5.0 and a SD Card with Route66 maps of the UK. I want to put a Europe or Benelux map on (doesn't matter wich one) but i'am totally stuck. I read some things about Hacking the device but it doesn't work for me (Maybe this isn't necessary). Who can help me on my way with this ?

If the device uses Route66 software, then you must use maps designed for Route66. Maps made for other software (iGo, TomTom....etc) will not work.
Your other option is to change the navigation software to something like iGo 8.3x or a 'lighter' version of iGo Primo. Then you can use any maps from here:
Maps-buildings-dem-POI.
If you decide that is something you want to do (change the software...which some may call 'hacking' but that is not really correct), reply and someone can probably help you...and a Moderator will move the thread to the appropriate forum location.