switching between dual hard drives

I'll provide a little more colour than USAFRet, though his advice is correct.

I don't know how much computer experience you have, so gonna start from the beginning. I mean no insult.

Your BIOS is the first piece of software the computer runs, making sure everything is working right and attempting to understand the right way to communicate with various pieces of hardware. At the end, it boots the Operating System (OS).

One of the things you can do in your BIOS is set where it attempts to boot from first. So, by default, you can make it look at HDD "1", and if it finds the Mac OS, boot from there. You can set up the BIOS further so you can hold a key, and switch another device to boot from. So if you hold the key, you can then tell the BIOS to boot from HDD "2", and it will boot up the WIndows OS, and you can work with Access. People call this "dual boot". This functionality also determines which order the boot drive checks for places to boot the OS from, and can include USB drives, DVD ROM drives, etc.

The mechanics of setting up the BIOS accordingly will vary depending on the actual BIOS in the MacBook pro - I'm sure there is a guide somewhere on the net to determining boot order of connected devices in the whatever BIOS comes with the MacBook. Sorry, in a rush right now or I'd find it for you.