When you purchase fonts, just like any other software, you actually purchase a license to use them on a certain number of computer devices (CPU’s). Please read the terms and conditions of the End User Licence Agreements (EULA) here. Fonts are licensed to use on up to five (5) CPU’s at a single location.  If you need to use the fonts on more than five CPU’s you must purchase additional licensing. The cost is based on the number of users.

256tm fonts are compressed as .zip files. Use Stuffit Expander for Mac, or Winzip for Windows, or simply click on the files to extract the fonts.

Installation on Windows:
Quit all and drag the font files to the WINDOWS/FONTS folder.

Installation on Mac Os X:
Quit all and drag the font files to the Library/Fonts folder (for every user of the computer) or to the User/Library/Fonts folder (to be the only user of the font). In Mac OS 10.3 and higher, you can also use FontBook to install the fonts.

Installation on MacOs 9.x:
Quit all applications and drag the font files to the Font folder in the System folder. You can also use Adobe ATM Deluxe, Extensis Font Reserve or Extensis Suitcase.

MacOs X font cache problems:
Delete the files in the folder Library/Caches/com.apple.ATS. In Mac OS 10.4, you can also use Tiger cache cleaner.
For Adobe softwares: quit all and delete .lst files. named "AdobeFnt"

To install and manage fonts you can also use a third party font manager. The freeware FontExplorerX is a good one.

For further technical informations, this myfonts.com page is pretty complete