Preowned Macbook

My wife has just bought a preowned Macbook with Lion installed. I want to reinstall the software to start with a blank page. I have the original Snow Leopard Disks that came with a previous Macbook that died to death so decided to install that first then install Maverick which she has purchased for an imac. Anyway, I rebooted, held the C button, the Snow Leopard disk showed up and asked me for the drive to install to. It showed the hard drive but with a warning triangle and stated that I couldn't install to this drive. I had previously tried pressing cmd and R buttons to try and reinstall Maverick on this machine but it wouldn't accept my wife's apple login details. So it looks as if it is locked into the previous owners apple id. As I see it, my only option is to format the drive, install Snow Leopard, put my wife's apple id in and go from there. The trouble is, what happens if I format the drive and I still get the same warning triangle? I will then be stuck with a Macbook with no OS on it.
If anyone has any ideas about my long winded blurb I would be forever grateful.

Thanks

Brian

If the SL disc you have shipped with a different model MB than the pre-owned one, it will not install as those discs are system type specific.

Can't have "purchased" Mavericks since it is free.

Since you intend upgrading it to Mavericks in any case, just re-download Mavericks on the iMac from the App Store, put it on a flash drive from where you can repartition/format the drive and do a clean install on the MacBook - assuming the preowned MacBook meets the minimum spec for Mavericks - which you should verify prior to spending the time to download it.

Minimum spec
Directions for creating a USB installer - here - I used Option 1.