Easy! :)

Windows:
(only Win2000/XP/Vista supported - earlier versions have limited OpenType and Unicode support)
1) Unpack the zip file (using the built-in unzip function of Windows, WinZip or any other unpacking utility)
2) Put the font file (ends with .otf or .ttf) into C:\Windows\Fonts
2b) Easy option for Windows Vista : Right-click on the font files > "Install"
3) Quit and restart any programs you had open (no need to restart your machine)

Mac:
(only MacOS X/10 supported - earlier versions have no OpenType and Unicode support)
1) Unpack the zip file (using the built-in unzip function of MacOSX, StuffIt Expander or any other unpacking utility)
2) Put the font file (ends with .otf or .ttf) into home/Library/Fonts
2b) Easy option: double-click the font file, then click "Install font" button of FontBook.
3) Quit and restart any programs you had open (no need to restart your machine)

Unix etc.
I have no experience with other operating systems, so you're on your own here - but if you have installed and use another operating system you're probably technically savvy enough to know how to install fonts ;)

As long as you have installed them correctly our fonts are shown alphabetically along your other fonts.
Except:
If you use Adobe CS programs on Mac you may find them at the bottom of the font menu - this is because the system (correctly) flags the fonts as multilingual, and so the CS programs sort them at the bottom part of the menu (where all non-western fonts are gathered). As all our fonts also contain the normal western character set they should not be sorted out like this - this is a "bug" that Adobe is aware of...

All our fonts are infinitely scalable; the limitations are in your software. A common problem is scaling fonts in Microsoft Word. If you choose Format / Font you can type in any number you like under "size".

At the time of this writing (Feb 2008) you can’t. After installing one of our fonts, you may be able to select it in your email application but the person at the other end won’t see that same thing unless they have the same font installed.
If you really want to use our fonts in email applications, make sure the people at the other end have the same fonts installed (but they will need to purchase their own license).

If you’re creating a web page using Flash, it’s easy. Consult your Flash manual.
If you’re using Acrobat, make sure the font embedding settings are turned on. Consult your Acrobat manual.
For anything else there are limitations:
If you want to use one of our fonts as your main, text font you’re pretty much out of luck unless you explore a font embedding tool such as WEFT but I don’t recommend it. To use our fonts as headings or titles, use image creation software such as The Gimp, Photoshop, Paint Shop Pro, Pixia etc. Save the images as GIF files and place them on your web page. There’s a lot more to it than can be explained here but there are countless books available on web page design.