bapu
No drive EVER reports the capacity listed on the box. It's a "format" thing. 43% is not bad. It's when you get near or under 20% of the OS drive that you should be concerned.
One thing about moving folders; if you have EZDrummer (not Superior) and you've installed the samples to your C: drive you cannot move that samples folder. You MUST uninstall EZDrummer and select the option of where to install the samples. This is true of EVERY EZDrummer add on pack. Big bummer, but that is the way it is.
Partially true... Actually, the box lists the capacity in decimal notation (base 10 - so 160 GB is 160,000,000,000), but the computer uses things in binary (base 2 - so 160 GB is 149,000,000,000). NOW you add in the formatting, etc. and you're going to lose more. Your 133 GB is still a bit low so there could be other reasons like a dead partition or two that you won't see unless you're in a disk management utility.
Anyway you cut it, even 160 GB is tiny now-a-days (but should be fine for an OS drive). So, if you can, I'd still recommend leaving the OS on your C drive and buying a larger drive as a second drive for your data. Personally (as I do with mine), I'd further make the first partition of the new drive match the OS drive in size (and leave it empty) so that I can restore an image backup to it if necessary. You'll want to have backup software like Acronys AND make a bootable backup CD. Then, if your C drive dies, you boot from the CD, restore to your newer drive, change the boot sequence in your BIOS and you should be back up and running. Once up, you should change the drive letters so the new partition is now "C" (note that the partition with your data should not have changed!). Finally, you'll want to get into the computer box and remove the dead harddrive and cables.