Depends on the pixels, resolution, type of card, etc. I have a 6.1 SLR....I use 1GB SD UltraII cards...I use the highest resolution and get less than 300 pics. All of my pics are very high quality.
The lower the res, the more pics you get. Also, it depends on the card. My camera that I used a CF card in would take over 500 pics on a single 1GB card on the higest res. It was a 4MP camera.
I might suggest you visit the website for whatever brand card you have and look at the Matrix.