optimum method to install win 8 with win 7 on T420

What's the best way to install win8 on the T420 along with win7 (dual boot)?

I've tried on the same ssd, on a second ssd, and on a separate hdd but can't get past the "Partitions" menu during installation. I've went through this but it didn't work. Installing Windows 8 Consumer Preview in UEFI mode in Dual boot with Windows 7 through bootable USB.

Suggestions?

 

Just to confirm is it a case where you can't see any drives available during the Partition section? Quite possibly it's due to the existing Windows 7 OS installed using the MBR (Legacy BIOS mode) format than the GPT standard required for a UEFI install. Though I can only guess at this stage as I don't have Windows 8 on me to test the theory out.

 

I installed win7 using UEFI and i believe the drive format is GPT.
When I try to install win8, it tells me the format is GPT that's why it won't install. The exact error i get is "Windows is unable to install to the selected location. Error: 0x80300024."