Dual booting 10.04 & 12.04

[Jim Byrnes]

I want to start moving from 10.04 to 12.04 by doing a new install.  To 
avoid downtime and have a fallback position I decided to put 12.04 on a 
new hard drive.  So I put in the new hard drive and swapped the cables 
from the 10.04 hard drive to the new one and installed 12.04.  I now 
realize that constantly swapping the cables will be a PITA and 
completely forgot about dual booting.

1. Is there a way now to have them both plugged in and dual boot?

or

2. Do I need to reformat the 12.04 drive and plug them both in and 
reinstall 12.04.

Thanks, Jim