There are 2 main ways to Make a Digital Picture Frame
1) Using a LCD screen and one of them picture viewers for TV's that read SD cards (these are about $10 on ebay now and then)
2) Using a Laptop to run it as a Picture Frame
Now with a laptop you can use any sized picture and have it fullscreen and in detail where a normal LCD screen with composite wont make your big pics from a quality camera show that much detail.
Now you can get a old 486 laptop if you want but i reccomend you get a goos 233mhz and above laptop to make sure you get a Active not passive screen and easily be able to run XP and wifi.
Now there are alot of cons and pro's on each type the laptop is really the better and cheaper option with the ability to either share a photo's folder over the network for it to read on the main computer to it downloading the pictures from a folder to the internet and storing it on it's own harddrive.
Id you really JUST want it for work and hooked up to the pc then look on ebay and you will see some nice 10" to 15" screens (the 15" screen just looks to big)
Install the LCD Screen into a picture frame and either buy a new video card or get a USB video card which when plugged in will allow windows to have 2 screens and you can have this automatically run something like Irfanview on the second monitor using the PC to control everything and if you did need the space you could drag the windows over to your picture frame and use it as a second monitor if needed

There are ALOT of ways to make a digital picture frame hell i setup my friend with one a 10" LCD screen from ebay that is used for the roof of your car (flipdown) and had it setup so he had a 2.4ghz wireless video sender connected to the LCD screen and was just using one of the TV picture viewers at his computer so he could just take the SD card out and upload new pics instead of going to the picture frame unhooking it all and removing the SD card
If this was home i would say the laptop route cause there is ALOt of things you could easily use it for like internet or as a universal remote control (touchscreen)
All depends how much u wanna spend I personally thing the LCD monitor as a second desktop in windows for your work enviroment is the best bet
