There must be something causing wrong managing your files on the C drive. Do you use Outlook? Any idea how big is your system's pagefile (right click on My Computer >> click on Advanced System Settings >> Click on Settings in the Advanced tab >> click on Advanced tab and see what is the xxxxMB count under Virtual Memory) ?
How much does the free space get in worst cases? If it is only as low as 5GB as you mentioned before, then it should be fine and there is nothing to worry about.
I suggest that you just leave it as it is and uninstall what you do not need from there. Don't use that C drive ever later and leave it for the system and updates only.
Because if you don't find the reason why the space (or memory as you call it) is being eaten, you will possibly have no solutions that do not involve losing the recovery files.
If it is okay to risk losing the recovery files, shoot us (not in the head tho
) and will give you many solutions.
Oh, no need to lose hope. Even with the recovery files lost, Windows and drivers can still be found on HP's website with some effort and good internet connection. You can then make your own recovery solution and save the 2GB taken for recovery on the same HDD that has Windows drive on it.
Note: spanning HDD's can only be done from within Windows and with all spanned-to-be HDD's unallocated. Yup, separate physical drives can be spanned into one drive only.