My last trip, I took 2 2GB cards, at my camera's best settings this worked out to about 450 pictures per card. I filled one completely, and the second one had room for about 2 pictures, lol! I need more memory!
My previous trip, I had an older camera with less MP, and so I took about 1800 photos with 2 512MB cards, and 1 1GB.
You say you have 7GB, but you need to figure out how many pictures that would be of the size and quality you normally shoot with (S, M, L, fine, superfine, etc).