You can put fonts directly into HD>Library>Fonts or in HD>Users>Your_User>Library>Fonts and they will be available to all programs. If you want to use a font management program, you can activate fonts only when you need them, and deactivate them when you are done. That will keep your computer running a little faster. Linotype FontExplorerX is free, or you could buy Suitcase or one of the other ones. Here's a link to Linotype:
http://www.linotype.com/fontexplorerX
Also, Quark 6.0 was the first release of version 6, and like most programs, there were errors that needed to be fixed. You should update to 6.52. Its free, and fixes many errors that you may encounter if you stay with 6.0.