I cannot access the desktop on my Windows XP installation. It won't even start on secure mode. I just want to know so I can install a Linux distro.
When installing elementary there is a use entire hard drive or erase disk and install elementary os option. This will destroy both your Windows installation and any files you have saved there.
If the above suggestions did not answer your question to your satisfaction ... try using a mini distro JUST used for partitioning a disk ... maybe try using gParted Live (I have no affiliation with it). I know this solution doesn't use Elementary ... but perhaps this will let you do what you want ... in case your question wasn't stated specific enough for us to offer another solution.