This link is to the thread for the 1 Gig
SD limit.
I tried a bunch there to get more than 1 gig SD working, but it just would not work.
But, there are many here that have used larger CF cards, 2, 4, and I recall seeing a thread here where someone mentions 32 Gig CF use.
The SD and CF are two different connections in the Axim with different drivers. So, they function differently (with different limitations).
The Axim X5 can work with larger CF cards than the SD cards.
Go out there and get the biggest CF you can afford; I just ordered a 4 Gig A-Data from Newegg.com, they have a rebate with it, and runs about $42 (before the rebate), and then I hope to get $10 back from the rebate.