Problems Installing True Type Fonts

I have been trying to install a number of True Type Fonts and have been unsuccessful which ever method I've used.
I tried copying them to the .fonts folder which worked the first time but not since then.
I've also tried going System-Preference-Font and copying them into the fonts folder but I get a message saying the fonts are already there (some are, and some aren't - the ones which are there don't show up on any of the programs like open office or GIMP).
I've tried copying them through the terminal into the shared users folder, but it says I don't have permission.
I've logged and and out and switched the computer off and tried again but the font just don't show up!

I must be doing something wrong but can't think what...
If anyone has any ideas I'd be really grateful!