Provided you can attach the SATA to your system, try using the DataGuard WD s/w they provide and make the "image" full copy back-up from old to new. However being what I believe is an old system, the SATA side may not be capable unless its fully OS loaded. As the DataGuard s/w in non OS required, though WD has different versions of this s/w. You can get the latest WD release and see if it works better or use your current copy. Basically, you have readiness issues not necessary the back-up as that can be done, but the h/w has to be ready to use the WD s/w under its requirements.
As for dual boot, that again is part of the OS and bios status. You don't need the bios to accept dual boot, but again you may. The OS itself can accept dual boot mode if the OSes differ, they can't be the same actual OS version or install. Under the bios, you need to enter that every time in order to direct boot mode. While some bios provide different boot modes(devices) they can lack that mode from multiple HDs, so be aware.
All these issues arise and you lack details in your post, so no clear answer. No one can answer properly w/o full details.
I have an older slow WD 40G PATA HDD and getting a new WD 80G SATA HDD.
I like to copy the existing HDD to the new one and keep the old drive with the OS as a stand-by using dual boot.
How do I goabout this.
I have WD Data Lifeguard and think it has the capability to move the OS to a new drive, but I am not sure if it lets me copy.