Yes, again, Main Memory is !!analagous!! to your RAM, ipaq file store is the same as Dell's BIS, and analagous to a hard drive, and your sd card is analagous to a cd.
I save my Outlook attachments to my sd card. Remember, the advantage of BIS/file store is that it's non-volatile, meaning that it won't lose the data with loss of power (dead battery). The disadvantage is that it's slower, and limited in space. An sd card is also non-volatile, and you can always buy a bigger one or more of them if you run out. Putting them into BIS (ipaq store) is probably unnessary.