What's the difference between each version of flex?

According to this page there's flex 1,2,3,4,what's the main difference between them?

Is there a version of flex that supports flash lite 2 which my project is using?

http://en.wikipedia.org/wiki/Adobe_Flex#Versions

So far as I know, no version of Flex are supported on Flash Lite. However, it may be possible to run a Flex 1 / 1.5 app on Flex Lite since they are ActionScript 2 based. But, Flex 1/1.5 had a very different licensing, pricing, and development model than Flex 2 and later. I'm not sure I'd want to do anything that predates Flex 2.

Your best bet is to not use Flex, but rather investigate building this app with Flash Pro.

Flash Lite 2 is not supported by any version of Flex.

As James mentioned corrrectly, no version of Flex supports Flash Light 2.