Hard drive advice?

[glatt]

I want to get a second hard drive for storing all my pictures. I've got some kind of large Dell tower. Optiplex or something like that. It's around two years old. Has an empty slot, I think. XP Home.

I'm fairly ignorant about my choices and the pros and cons of them.

I know there are external ones that must have USB connections. They seem like they would be simple to set up and might work with a future machine more easily. Might be slower though.

Then there are internal ones which might be tricky to set up but maybe faster/ cheaper?

I really have no clue. If you were looking to get a second drive, what would you look for? Which brands are good brands? Which are bad? What's a decent brand for a decent price? I'm guessing around 200-500 GB would be good, but don't even really know that much. Have 80 GB now, but it's filling up fast with two newer higher pixel cameras.

Please educate me.