I figured it out.
There is a switch on the side of the card to select
the 3 positions noted above. This information should
have been shipped with the card. It took a while digging on
the sandisk web site to find this information.
I finally found a pdf describing the switch. A big
red flag is that if you change the switch position,
to use 4 GB (from the sandisk pdf):

"When you switch to position #1 all data on the card may
be lost. Even if the data is not deleted, it will not be viewable
in position #1. Please save data to a PC before
switching to position # 1 (4 GB)."

So what happens if in the field you accidentally switch from
position 1 to 2 or 3? Do you lose all your images?
Has anyone had a problem with this switch?

The flimsy feel of the switch to me means this is the
last one of these cards I buy.

Roger


That does sound rather weak, but at least you will only use it once. For the
record, I've been using a (switchless) Ultra II 2 gig for about six months and
have zero complaints.