Sam,
I think you are mixing a couple of symbol types here.
There is a MapBasic tool called Symbol Maker that helps you creating a MapInfo 3.0 Compatible symbol. This new synbol will be stored in the MapInfow.fnt.
The MapInfo 3.0 Compatible symbols are somewhat limited, so you will easily reach the limits.
I would recommend that you use either a True Type Font symbol (TTF) or a Custom Symbol (a .bmp file and with MapInfo 9.5 are wider range of filetypes).
In your case where you already have a "picture" of your company's logo I would choose the later, the Custom Symbol.
If you are using a later version of MapInfo Pro there is almost no limit to the filetype and zise you are using. The later versions even have a Add button in the Symbol style dialog that you use to add you own bitmaps (pictures) to the list of MapInfo Custom Symbols.
Otherwise you would have to manually copy the file with the logo to the custsymb folder located under C:\Documents and Settings\username\Application Data\MapInfo\MapInfo\Professional\950\CustSymb where username is your Windows username.
Also note that with MapInfo 9.5 you can even create your own folder within this folder, and you can in your preferences point to a location on your servers containing these symbols (and other program files)
Peter Horsbøll Møller