Best way to work with Flash?

I’m starting to learn Flash and I don’t understand which way would be the best in terms of web app design and development. I want to make a slide show with labels you can toggle on and off.

i see all this stuff about Flex2 and MXML etc. is there something wrong with Flash CS3 that you need to use Flex2?

which one should i use? i guess since i’m new i should start with CS3