Disk Utility is strange

While I was installing Snow Leopard I partitioned my 500 GB HD in 2.

Now I want to install win 7 and I've relized that BootCamp will care about partition, so I would restore the original situation merging the space in one partition.

I did it with disk utility, nothing of easier, but now I have a strange situation:
It tells me that I have

Free Space : 61,42 GB (61.416.329.216 Byte)
Used space : 18,98 GB (18.980.089.856 Byte)
Capacity: 500,000 GB

So I have all the Capacity but I can't use the space (in fact BootCamp let me split only 61+18 GB)

This is my situation (it's in italian but the bottom right part it's easly understandable):