This is a bit of an odd one for my first post here ^^

I have a friend who has XP installed on her PC. She decided an upgrade to Vista (64bit) was in order, so she did. By buying a new HDD, removing the original and installing Vista on the new drive ><

She now uses both OSs, by opening up her case and swapping the drives over before booting.

Now, the question is this: we have 2 hard drives with an OS on each - if both HDDs are installed, how would we enable proper dual booting?

Any tips and advice gratefully received

You can install a boot manager like EasyBCD.
Download EasyBCD 1.7.1 - NeoSmart Technologies

Or you could change the boot order in the BIOS (setup).
Most newer systems also have a key, like ESC or F8 etc, that can be hit during the POST to choose a boot device.

Or you could put Vista in an external enclosure, set the first boot device to external, then simply unplug or turn off the external when you want to boot to the internal.

With the operating systems all ready installed....use the boot manager as S&M pointed you to. It is really simple to use... Install the boot manager to either of the drives and then install the other drive and all will be well. Adjust the time for display of which system to boot to ( I like 20 seconds) and then the default Operating System. When you boot up it will display the dual boot menu for time period and if not used will boot to the default operating system.

The boot manager will also allow for future additional drives without interfering with the ones all ready installed.

Thanks for the speedy response, guys! I had seen mention of EasyBCD but wasn't sure if it would solve this particular problem.

I bow to your wisdom