You failed to mention the type of card.

But since the HP320 uses SD type memory cards,
I assume you have 512mb SD cards.

Trying to find out the maximum capacity of a media for a particular camera is very difficult. They never put that information in their specifications.

If you go and look at the Canon Power Shot A400 you will find that it uses SD memory.
I checked under "Supplies and Accessories" and they show 64, 128, 256, 512 SD memory cards.
So I assume it can use 512 SD memory cards.

You can double check by visiting a store that will let you get your hands on an A400. Bring your 512mb card with you.

The Canon A400 sells for under $150.
It has a sharp lens and takes good photos.