There are several things you need to come to terms with as to fonts and Gerber software.
1. Gerber uses a proprietary font system and comes with its own fonts. They are installed along with the software initially in a folder named GSPFonts. They have a file extension of .GSF and the names all start with the letter "G". So if you can't find your fonts you need to either locate the GSPFonts folder and transfer it to your new computer or you need to reinstall GA6.0 from your original CDs.
2. Gerber supplies a utility program named TT Font Converter. You can use it to convert any TrueType font to Gerber's proprietary format. It offers a choice of two ways to do it: Convert or Disjoin. Using the convert routine, the font is simply converted and its kerning and spacing scheme are retained. The resulting Gerber font will be faithful and of as high a quality as the original font, however, the ability to modify spacing (tighten or widen) in the Gerber font will not be available. This works fine for connected scripts but may be missed with other fonts. Gerber font names created by conversion start with the letter "T" when viewing the actual file in Windows Explorer. Using Disjoin, breaks all the characters down into individual PLT files and then they can be easily reassembled into a fully functional Gerber font using a second supplied utility program called Font Designer. It does a beautiful job on every kind of font except connected scripts. Gerber font names created by Font Designer start with the letter "U" when viewing the actual file in Windows Explorer. I wrote a tutorial on using it which is located
HERE.
You should also be aware generally that you are using software which is about 15 years out of date and is only a 16 bit application. As such, you will encounter an increasing number of difficulties as you attempt to run it on an OS newer than Windows 98 or, in general get support for it.