This software has been tested and runs on WinXP, Win 7, Win 8.
Extract the zipped file to a folder of your choice; you should be OK.
If not, this may mean that you do not have DirectX. In this case download and install DirectX9.0c or DirectX11. You can use the web installers (dx09websetup.exe and dx11websetup.exe) included in the zip file; or search "DirectX download" in Google.
VERY QUICK START
In the folder where you extracted, run FLOW GUI.exe and click the GO button. A new window should come up containing the walkers, who will start walking. For more details open FLOWQuickStart.pdf.