On the Sony site it looks like the most you can get is 128MB for that camera.
here's the chart page and more info.
http://esupport.sony.com/US/perl/sup...=12&mdl=DSCS75

and it sounds like this is needed also-
*4 = A dedicated adapter (MSAC-M2) must be attached to use Memory Stick Duo™ or MagicGate Memory Stick Duo media.

I don't know if it would be cost effective to buy more memory sticks and an adapter for this camera - might be cheaper to find a new camera on sale.