I get mine from Windows Vista. c:\windows\fonts\
and I use FontExplorer freeware to preview them.
http://www.moonsoftware.com/fxplorer.asp
Then create a folder \fonts\ on the SD card and drag whatever fonts you want into that folder.
I know txt and rtf formats support changing to a user selected font via thePP. I just wish I could figure out how to change fonts in .pdf though.