Right, you have a 6 megapixel camera, Depending on whether you shoot RAW or your largest JPEG which is about 2.5MB you need a CF card larger than 2GB - this is because if the card is over 2 GB you camera recognises this automatically and adds FAT32 support - don't bother about the terms or understanding how it works - it means simply a card over 2GB with work faster and better in your camera. In your case I would go for a 4GB card - At Jessops a Sandisk 4GB Extreme IV Compactflash Memory Card is £33.20 This will give you about 400 shots in largest JPEG, over 1000 in smallest JPEG and about 150 in RAW. Please do buy from a reputable dealer. You can get them cheaper on ebay but there are numerous stories of fake cards that are not worth the money you think you save. By the way the speed of you card would only effect wildlife if you were in burst mode trying to track a cheetah
