You've come across one of the drawbacks to designing web pages, and the reason why so many sites use Verdana, Arial, et al (sans serif fonts being considered easier to view). It's because these are generic Windows fonts, and likely to be on most users PCs.
If your code looks like this:
font-family: Verdana, Arial, 'Century Gothic' sans-serif;
This is how the browser will interpret it: Look for Verdana, and if this isn't installed on the viewer's system then look for Arial. If this isn't installed, then try Century Gothic. Failing this, use any sans serif font that the user has on their system.
Note that if you're using a font containing TWO words, then you need to enclose these in single quote marks, as above.
Hope this helps.