How to back up all my (custom) fonts?
All your fonts should be stored in the C:/WINDOWS/FONTS/ directory (and all its sub-directories). I suggest you back up all of that, and then preview your backup copy to be sure that all your fonts were actually copied.
Do note that it's possible for fonts to be stored elsewhere, but this is extremely rare. If you do find that something is missing from that FONTS directory, then please post and update back here.
Copying the fonts back into the C:/WINDOWS/FONTS/ folder doesn't always work properly. But, what you can do is select a number of fonts, right-click on them, and then choose the appropriate "Install font" option to get them installed. You should also be presented with an option to copy the files to the FONTS folder (I recommend you do this so that your FONTS directory will contain copies of all your fonts).
fonts folder = \windows\fonts (usually)... just copy files from there. note that you need admin right to write there.
to check if the font is installed with windows or custom installed, try to use the datestamp (e.g. dir /od in command prompt)
Because of the special format of the fonts folder when you open it in Windows, you may find it easier to use a different file manager, particularly if you want to zip them all. What I did is I opened the 7-Zip File Manager and browsed to %WINDIR%\fonts. I then selected all of the font files (Ctrl+A), and chose File > Add to Archive to create a ZIP file with all the fonts. You can also use Copy To on the File menu to copy all the fonts to a backup folder.
When you go to restore the fonts later, you should make sure to install them properly. Unzip the file of fonts, then select them all (in Windows Explorer), then right-click and choose Install.
In the past, my downloaded fonts were able to be saved on a flash drive, so I'm assuming you could do the same in your case, via drag and drop: http://windows.microsoft.com/en-US/windows7/Move-and-copy-files-using-drag-and-drop
I needed to copy 1000 fonts from my Vista machine to my new Windows 7 machine. I used 7-zip as suggested but just used the "Copy To" command in 7-zip to copy them to another folder, then I copied them across the network. Worked like a charm.