As in sync to the droid or sync away. I use itookthisonmyphone.com (android app available in market) to sync all the photos I take with my droid(and did with my blackberries too) tot he web for easy access. To get them on your droid, plug it into your computer, mount the usb drive and have at it.
Or, if you want to keep imported images separate from ones you take using the Droid's camera, put them anywhere you want on the SD card. They'll be picked up in Gallery and you'll see them there.
I've added my own folders to my SD card for ringtones, notifications, images, video, you name it, I have a folder for it.
You can put media files anywhere you want on the SD card, and the phone will put Droid created media files there too, in folders it creates.