I believe that the Nikon D40 is both SD and SDHC compatible. It should be capable of handling SDHC cards to 32 Gigs, but those are very expensive. The other consideration is how many images you could lose if the card fails or gets lost.
My recommendations is to purchase a whole bunch of 4 Gig cards. These fit nicely onto a standard single-density DVD format, making backup easier too. Also purchase a couple of memory card wallets. Store the spent cards upside down and with the card switch set to read only so you can't accidentally erase images. Put one wallet in a safe place and only carry enough cards for the day's shoot in the other wallet.
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My recommendations is to purchase a whole bunch of 4 Gig cards. These fit nicely onto a standard single-density DVD format, making backup easier too. Also purchase a couple of memory card wallets. Store the spent cards upside down and with the card switch set to read only so you can't accidentally erase images. Put one wallet in a safe place and only carry enough cards for the day's shoot in the other wallet.
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