I did it and 't werkt:
1. Do a full install as described in: http://samsungi8510.com/forum/feb-2009-i8510xxib2-free-download-drivers-instructions-t807.html
2. Download this package, it contains a dutch csc: http://www.megaupload.com/?d=ZNNKEMSO
3. Open apollo 6.05 (not 5.27) and click 'pda image' -> choose 'presettable_kpn.xml' in the i8510xxhj3 folder
4. Choose 'CSC' at pda-status
5. Turn on your phone with 1 and 4 buttons pressed
6. Connect usb cable and click pda-download
After flashing test by typing *#1234# in your phone.
Firmware is really a lot faster, to make it even faster goto themes -> options -> theme-effects -> off. (it's enabled again due to the csc flashing)


