PDFs of manuals are usually available on Nikon's support site. Here's a link to the D80 manuals.
The D80 is an SDHC device, so only use SDHC cards in it. It's safer and will save you some money. The SDXC card might work, but the camera would format it as if it was an SDHC card and would not be able to take advantage of any speed or capacity improvements that SDXC offers.
Speculative buying is dangerous. You should use what you've got first and as Suzy said let that tell you what you may need. About the only "safe" extra purchase would be a card reader if you don't already have one and you don't have an SD slot on your computer.