RE::"Hi, i need to move some files on a hard disc in Knoppix, but when i do it tells me "Could not make folder /mnt/sda2/.."

Had to reply because it doesn't seem this got resolved for Simonkex. I discovered this little nasty with a Flash Card inserted into a USB port.
To make it short:

Plug in the Drive and wait till it pops up on your desktop.
"Right Click" on the Drive Icon and "Mount" from the Menu that pops up.
"Right Click" again and choose "Actions", and from the next Menu choose "Change read/write mode".
A window will pop up asking if you really want to "change partition... to be writtable?"
Click "Yes". (All this assumes the Drive is NOT formatted in ntfs)

Now to verify everything is as it should be: try writing a new Directory to the drive -- if it works, you're good to go.

I discovered the USB drives weren't automatically writable when I directed a download to one

I've used quite a few different Distros of Linux and I really like Knoppix (almost everything works great)...
Only time I was really ticked was when trying to save a "configuration" to floppy and discovered I couldn't
get it to re-load on startup. The startup command was wrong in the documentation -- it should be:
"knoppix floppyconf" NOT "knoppix myconfig=/mnt/auto/floppy"