Interesting that you've found an all-5V camera. I've got several, from some of the first to the newest, and all of them make use of a 5V voltage regulator built into the connector that either hooks up to a 9V battery or a wall wart, and sends both voltages to the camera. For these, my suggestion is to get one of the battery eliminators that Micro-Mark sells just for these cameras. I've built four cam-cars; the last one is powered this way from DCC and works quite well.
For a camera that runs on all 5V, all you need is a 5V regulator, a rectifier and a filter cap. You can get the regulator from places like Digi-Key (http://www.digikey.com/). They have three pins, like a transistor: ground, input voltage, and output voltage. Although it sounds strange, you could possibly get the Micro-Mark unit and replace the regulator with a 5V version (they will be the same size package, and the pin connections will be the same). Then you'd have the whole circuit, complete with rectifier and capactor, on a pre-made circuit board.
EDIT: FWIW, here's a photo of my latest cam-car:
[img width= height=]http://lh4.google.com/dks2855/R5vG77QVsnI/AAAAAAAAD0k/dEI4d66dX-A/s800/IMG_2150.JPG[/img]It has the Micro-Mark battery eliminator, with the camera's own 5V regulator carefully extracted from the connector and soldered right to the Micro-Mark board. The chassis is from a Kato caboose, one of four strung together to provide 32-wheel pickup. Not shown is a lead counterweight to keep the car from tipping forward.
