Switch between 1.6.6 and 1.7.2

This method can work with other versions of minecraft also but I have not tried.
Why? The scenario I had was the only minecraft server software that had a GUI, I could get was 1.7.2 and I had a mod loader for 1.6.6. To play on my server I would need to update to 1.7.2 and loose my mods (not good).

OMG What Did You DO 0.o? Simply the core minecraft files [windows don't know about the others] are just 5 .jar files in the bin folder in .minecraft. To be able to switch between the two, copy all the .jar files in "bin" and put them in a folder called 1.6.6 [assuming you have not updated yet], then update to 1.7.2 and go into the "bin" folder again and copy all the .jar files into a new folder called 1.7.2 . And to switch between 1.6 and 1.7 just copy the files from which version you want to run into the "bin" folder eg: to switch from 1.7 to 1.6 copy the content from the folder "1.6.6" into the "bin" folder and replace the files or visa-versa .