My hard disk suddenly filled up and I can't find the files

Question

that are causing my hard disk to fill up. I was watching some videos that was on an external drive on my computer using vlc. I finished one movie (.avi file) and then tried to watch the second one in the series. However, the vlc application would not open it. I tried several times. I gave up and tried opening it with the quicktime player. Even though it opened, I got a message that my startup disk was full. That was strange because I am sure I had about 20GB as I was keeping a close eye on my hard disk capacity. I had recently deleted many video files and so I had a rough idea of how much hard disk I should have.
Anyway, I deleted some movie files to make space and then I checked my hard disk with Disk Inventory X.
When I did that, I found some strange files.
There are some temp files some of which are 1GB. The path is private/var/vm/tmp. One file is labeled a Quick Time player launcher document.
Another one is called "sleepimage". Format is HFS+. It is 4GB. It was modified recently (yesterday). Its path is private/var/vm/sleepimage.
I don't want to delete anything important by accident.
I just think this is strange and want to find these files but when I click "Open", it says I don't have permission and I have to locate them in Finder. However, when I type "sleepimage" in Finder, nothing comes up.
I really want to get rid of any files that take up a lot of space on my computer and that shouldn't be there. Do you think this is some kind of virus? And that's why my computer is filling up with some strange files. There are also many swapfile documents that are 1GB in size.

Answer 1

I think the problem is Quick Time Player. I am using OS 10.6.8 by the way.
I tried it out again.
I had about 26 GB of space before I played an .avi video.
After the movie started to play (it was slow to load), I got a warning message that my startup disk was full. I opened Disk Utility and it told me I had no space left (about 20 MB or something like that was left).
I watched to the end of the movie.
Then I quit Quicktime Player.
And I shut down the computer.
I turned on the computer and checked Disk Utility. I have about 26 GB of space.
I think for some reason Quicktime Player uses up a lot of the disk space when it runs movies that are problematic. This movie I was watching did not open with vlc.
I normally use vlc to watch movies.
Probably it doesn't use up this much space when the movie is OK.
I think there's a problem with this particular movie. It is about 50 MB so it's not that big a file. I watch .smi subtitles with it. The Quicktime Player automatically loads the subtitle file in this case because the subtitle file has the same name as the movie file.
I watched about 10 movie files from the same series that I downloaded together and did not have any problem watching them. I watched them on vlc. But this latest movie had problems I think (as I repeat). It did not load on vlc even though I waited for a minute, and normally movies load instantly on vlc. 
So I think that movie file caused problems. It made QT player use up a lot of hard disk space.
I had better avoid watching that movie in the future. I don't want it to wreck my hard drive.
So to sum up, everything is back to normal. I have the hard disk space that I should have. However, I am scared of damaging my hard drive due to shonky movie files that eat up all the space when they are played using QT player, and so I will not watch those files in the future, as I do not know why the files do that.