Dual Boot With Two Separate Drives Vs Partition

I have read that using a computer specifically for financial transactions with known and trusted entities (such as a bank) is a good way to reduce (though not eliminate) the risk of your accounts being hacked by reducing the likelihood of inadvertently installing a malware, spyware, or virus by reducing internet sites visited. Assuming this is correct, I was wondering about dual booting one computer with two physical hard drives (each with its own OS) versus one hard drive with two partitions. I figure the former would be "more secure" since one drive would be isolated from any unwanted programs. However, since they shared a few things (motherboard and such), is this set up as "secure" as having two computers? If so, how does one go about setting up a dual boot with two separate hard drives of the same operating system using one computer?