It is not likely you have to do that because there are very few things that run on W7 that don't run on W8 (I had no problems with any of my programs I ran on W7 when I migrated to W8 - they all worked just fine).
The virtual machine became popular when people wanted to run ancient XP era software on their W7 systems that W7 did not support. This was a problem because the W7 was so much different from XP.
I suggest if you are worried about a particular piece of software, visit the maker's site and see what it says about W8 compatibility.
I have been told that I can run my old pc as a virtual machine on my new pc
To be clear, you are not running "your old machine". You are running your old operating system (W7 in this case) in a virtual environment. And understand to do that, you MUST have a valid Windows 7 license for this new machine. If your current Windows 7 license is an OEM license (as it most likely is) and came with your old computer, you can NOT legally use that on your new machine. You would have to buy a new W7 license.
So unless you want that extra expense too, I would check to see if your programs are supported by W8 first, and since they already run in W7, they likely will run in W8 too.