Something else to check quickly.
I got a Toshiba 2Gb memory stick a while back, and I recall having what I thought was a similar problem.
My computer recognized the memory stick as TWO drives, one being 4.1
mb, and the other being 1.85
Gb
It took me a while before I realised that the 2nd part of the unit was available, as I was trying to save to the first bit.
I've just looked at it again, to confirm, and it shows up as:
U3 System (J:) capacity 4,325,376 bytes
Toshiba (K:) capacity 1,993,932,800 bytes
My last memory stick, smaller, was just recognised as one single drive, hence my confusion. (or maybe that's down to my age

)