"Parameter is incorrect" shrinking volume

[Doodle]

Hi guys, I'm trying to shrink my hard drive (500 GB) so I can try out Mandriva OS but I can't, whenever I try to do so i keep getting parameter is incorrect. Any suggestions guys? Running Windows 7 Ultimate 64-bit. Oh yeah, consider this my 2nd question, before I was trying to make a new partition I tried installing Mandriva via the disk, but it filled like 50 GB worth of files and I can't find those files.. All suggestions welcome

 

[whs]

1. What number did you specify in the wizard as amount that should be shrunk.

2. Your life will be a lot easier if you try Mandeiva in Virtual Box. I run Ubuntu that way and there is little difference to native mode. The big advantage is that I can run Win7 and Ubuntu at the same time in parallel.