A litte late to the party, but Frag had a great idea on how to do it.
Here's a little nifty back-way in GIMP, if your familiar with it.
Seperate images. First, select file>open as layers. Then, select all your image's (shift click), and import them. Now you'll want to head to Filters > Combine > Filmstrip.
Here you can leave all the base settings, and click ok. It will generate a perfectly spaced long image on a film looking layer, including all of your photo's.
After this, you'll want the layers option at the top. You'll want to click add layer, then make sure it's a transparency, and click ok. Now, you'll want the same option, and select merge down.
When that's done, you'll want to grab the RGB select tool (looks like a pointed finger on the toolbar), and shift click the black, and white areas around your images (part that looks like film), and hit delete.
This should leave you with a well spaced, single row of your images.
Also, you might try googling "Glue it". this is a wonderfully small, free program, that will automatically allow you to add individual sprite pictures, and assemble them in order (based of what they are named (just remember to name files 1, 2, 3, ect) in order), and create nice little quick spritestrip.
Sorry for the mouthful, but don't let all that turn you off. After your used to it, you can do all those steps in about 30 seconds without a problem .