Originally Posted by Koyae
my USB-drive (from which I'm running MEPIS right now)
Because of your poor choice of thread title, I think those replying to your question missed the key detail (IIUC) that you are booted on a USB memory stick, not on a CD.
So your question is not the usual: how to get the liveCD out of the way in order to use the CD drive for other purposes.
Your question is which preinstalled programs to use in Mepis to copy data from a Windows partition to a writable DVD, and how to use those programs.
I didn't happen to know the answer to that, but "k3b
" suggested in the previous post looks like a good suggestion of at least what documentation you want to look at.