Connect and select your iPad on the left-hand side of your computer's iTunes, and on the right-hand side there should be a series of tabs, one of which should be Photos - if you select that tab you can then select which photo folders to sync to the iPad. There is a bit more info on this page. You will need to sync all the photos that you want on the iPad together in one go as only the most recent photo sync remains on the iPad - not including photos in a subsequent sync is how you delete them from the iPad.
When you sync there is a Photos category. If you don't want to sync photos to a program, switch it so it says Sync Photos from Folder. Then show it what folder on your computer you want to upload photos from. You can make a folder of photos that are only for the iPad, and sync the iPad to that folder.
Another way. You can use a USB flash drive & the camera connection kit.
Plug the USB flash drive into your computer & create a new folder titled DCIM. Then put your movie/photo files into the folder. The files must have a filename with exactly 8 characters long (no spaces) plus the file extension (i.e., my-movie.mov; DSCN0164.jpg).
Now plug the flash drive into the iPad using the camera connection kit. Open the Photos app, the movie/photo files should appear & you can import. (You can not export using the camera connection kit.)
Thank you. Thank you. These few words, along with King_Penguin's, above, solved my problems of dissappearing photos when I changed sync parameters and my iPad's blindness to photos on my SD card, despite following instructions in the user manual.
I'm baffled at Apple's reputation for user friendliness despite such hostile behavior as this.
-a new iPad owner