Loading pc fonts to a mac

Can anyone help me??
I figured out how to load fonts on to my pc at home.
I use a mac at work. I tried to load the fonts into the mac and it didn't work. I first tried downloading the font the usual way way done on the pc. I then unzipped the file using Stuff it Expander. Then I put the font into my fonts folder in the systems folder. Then I opened ATM and put it in and quit ATM. I then re-started Quark and the font is not there. I also opened Word and the font isn't there.
Is there anything I need to do to the font to allow the mac to read it?

Be sure to check the following:
1. make sure the fonts are mac fonts-not windows
2. make sure you quit all applications before moving fonts into the system folder
3. ATM doesn't require the fonts in the system folder-you can do one or the other!
Give those a shot and let me know what happens!

Leelee I have to put the fonts into ATM. I have been told 1000x by MIS to do it this way. I know an easier way. But noooo can't do that either.
I think the fonts are Windows fonts. How do I convert them to MAC fonts?
Someone said something to me about true type font. Not sure what that means. But the fonts I downloaded off of a website have the extension ttf on them when I looked at them in the fonts folder on my pc. I take it that is true type font?