cant overwrite files on external hd when on another computer

Hey,

I have an external hard drive that I use to transfer files from home and school. At school I cant overwrite my files on it for some reason. I looked in the properties of the drive and I dont see anything that says some time of protection... is it possible that there was something like that when I formatted it?

any help would be great, thanks.

 

I may be to do with the caddy driver on school's pc which needs updating.

 

do you think it might be because I formatted it as ntfs and not fat? My friends have fat drives and they work fine.....