someone suggested 2 hdd for 2 OS, but I hadnt considered separate drives for OS and data. Sounds like a good idea. Does having them separated change the processing speed? Do you need to change your power supply and/or hardware or software? Is it expensive?
I've never noticed any change in processing or access speed, and there's no need to change any software - Windows recognizes the second drive, lets you format it and gives it a drive letter with no problem.
Depending on what your computer has built in, you might need to buy a controller card for the second hard drive, but most systems these days have connectors for multiple drives. My current Dell has a connector for another drive beyond the two I already have installed, should I need more space. There's a chance you might need to upgrade your power supply, but that's not an expensive or difficult upgrade. I've only needed to upgrade the power supply to support addons once or twice, so you're probably safe. If the computer has the extra bays for more hard drives, it probably was designed with a little room to grow in the power supply as well.
Another advantage to using multiple drives is you wouldn't have to keep all your data on the virtual machine - stick it on the second drive, let the virtual machine see that drive, and you'll have your data accessible to both the guest OS and the host. Then you could have the host OS back up the virtual machine and your data. If something corrupted your virtual machine file, your data would be unaffected, you could restore the virtual machine and get back to business with no data loss.
Basically, I'm suggesting you do a two hard drive system, with your host OS and virtual machine on one drive, and all of your data on the second drive. Back up your data on a weekly basis at least, and back up the virtual machine when you make a change - adding a program for instance.