Yes, create a playlist of said songs, highlight that playlist, select everything in that playlist, then drag it to a folder on the other drive.
The only difference on my list between ripped from CD and not-ripped-from CD is that ripped CDs for me are 256 Kbps VBR MP3. So I can do a smart playlist where Kind is "MPEG audio file" and bit rate is "greater than 130 Kbps" (VBR can confuse iTunes, so specifying 256 doesn't work.)
If you specifically want to back up JUST purchased content, iTunes has the ability to do that to CD/DVD, but not hard drive. It's under File -> Back Up to Disc. If you want to make your own, make a smart playlist with kind "Purchased" and "Protected", those cover both the iTunes Plus non-DRM and the DRM ones.