You need a piece of software to convert a series of images to a video file of some kind. Photoshop is not that. You said flash below, but maybe just start with turning jpgs into an avi or mov, and then look for a flash video encoder / converter (there are lots of freeware ones I suppose).
Search google for time lapse jpg to movie or jpg to avi or something. There are some freeware and shareware programs. I've never tried them. I suppose many are focused on automatically CAPTURING images, not necessarily converting them to video, so look carefully.
Alternative, if you have a video editor of some kind, then you can create your own time lapse movies. I use Sony Vegas to edit video, and you can easily create time lapse videos with it. To do so, you do this:
1. Order your files into one folder (if you're using lightroom, just setup the order you want in a collection, and then export to a folder using "index" for filename option). You'll be left with a folder of files like this - 0001.jpg through 9999.jpg or whatever you chose for the index number.
2. Open vegas
3. Import the folder full of index images. There are a couple of ways to do it, but I usually just import all the images individually.
4. In Options->Preferences->Editing, set the default still image length to the number of frames / amount of time you want for each image.
5. Select all the images and drag them into the timeline.
6. Render the movie in your preferred format (Vegas doesn't support FLV as far as I can tell, though maybe there is a plugin or something, and certainly once you have a mov or an AVI you can encode it to FLV later).
Good luck.
Eric