If you would like to know the technical differences between Type I and Type II Compact Flash please look at the following link.
http://www.compactflash.org/faqs/faq.htm#What_is
Simply put, the easiest answer is that CF II is slightly thicker. A CF I card will fit in a CF II slot, but a CF II won't go in a CF I slot. The Axim sleeve takes CF II cards, so in theory CF I will also work.