Did you just extract the font directly from the zip / rar file? If so, I always go into the actual Font file in the windows and hit view and refresh, it lets you use the font without restarting ps. Dunno if that helps at all, but incase!
I know if i unzip directly into the fonts directory it never seems to work correctly. If i unzip to a temp folder, then copy/paste it into the fonts directory it goes through it's little installation, and then i can use it in photoshop.
Not sure kyo, I think you have to just restart PS to use the font, unlessssss you refresh.
And tombo, your right, when you directly extract it to the font file you do either have to restart ps or go to the font folder and view > refresh
Not sure why, but oh well!