I dont know if your approach is necessarily the best for what it is you seem to be trying to do here.
Having two partitions on 1 disk isnt really a great protection against losing your files in the future, what about disk damage? How did you lose your files on it first time round?
Anyway - to help you with your question - it sounds like you want to do this on the fly without reformatting. Id say this is another bad idea but anyway...
Why this whole thing is a bad idea:
-What are you defining as the minimum required space to run windows?
-You already have programs installed in program files, are you planning on keeping these on the c drive?
That would assume then that you never plan to install any programs in the future which will eat up your fixed and limited space. (Whats the point in keeping program files folder safe anyway? - the programs wouldnt all work if you ever reinstall windows - you would have to reinstall the programs - think registry entries etc - so this says to you you cant define a minimum space unless you never want to install any programs in the future)
-What about your Users directory? Is it moving drive? This can have horrible hangovers if done on the fly
-You may be considering moving the current program files folder - this could be a bad idea and also have hang over effects later on
This crazy fella has carried out what you seem to want to - would be a good idea to read his experiences and opinions.
For resizing your partitions on the fly I would look into getting a bootable disc with gparted or something on it.
Why dont you invest in another physical disc and reisntall windows afresh using this other disc for your personal data and leaving a full hard drive for windows and however much space it will need - dont confine your options too much - it will cause pain one day.
You would of course also be advised to back up this other physical disc :)
In saying that your whole sitution could probably have been avoided if you backed up your files anyway :p
To check if the d: drive is formatted go to "Computer" and double click on it - windows will alert you if it needs formatted.