XP doesn't read correct size of my hard drive

Hi,
I have XP sp3 and a 500 gig hard drive . I like to collect videos of concerts and I am up to 475 gigs on my main drive where the system also resides. 200 gigs of that are videos, the rest are MP3s.
I also have a 2 TB external drive so when I saw that the main drive was almost full I moved my videos to the external drive. To my surprise XP under the c: drive properties still shows 475 gigs used....no change!
Then I went into the folder of the C:drive then I selected to show hidden files and I select everything in it.After that I opened properties and the result was 278 gigs used which sounds about right.
My questions are the following:
#1: Is that fixable for someone like me who doesn't have a computer science degree?
#2: If I accumulate an additional 25 gigs will the computer then see the disk as full?
#3: If that happens will I have problems or is there some workaround?

My system is not FAT but the other one NTFS ( is that it?) I would very much prefer if there was a way to avoid having to reinstall windows and start over.
Can you guys help me?

 

http://www.ilounge.com/index.php/ar...your-itunes-library-to-a-new-hard-drive/P100/

read above, there is evidently a special way to move music files to a new drive.

let me know if it helps

and also, windows requires at least 15% minimum to operate , if it is not there lots of programs will not work because there is no space.

 

Thanks for trying to help. My question had nothing to do with moving my I tunes library.
And yes I know about the need for windows to have a certain amount of space, I just wasn't sure how windows determines how much space there is. Like I said The C:drive reads one thing and the content when I select it reads the correct space.
As it turns out, it may be a Rollback RX issue. I didn't mention I had this program installed because I didn't think it mattered. RX is a program that takes snapshots and saves them as restore points. I'm going to set a new baseline once i know everything on my hard drive is good. Then I can delete the old restore points and then the drive space might be back.I hope

 

Okay let me know if this works or not,

Also read here on how to determine space on disc:

http://www.computerhope.com/issues/ch000369.htm