Microsoft Visual C++ itself is a commercial product and unless you wish to search for it illegally (an act I do not condone), then you will have to be ready to pay the hundred dollars or so the program costs.

In the past week, Microsoft has released Microsoft Visual C++ Express which is for now a free download, since I believe it is in beta stage. The Express range is an introductory point for beginners so I am unsure as to whether it will be fully compatible with the HPB_Bot source code. Also, you might want to check out the accompanying EULA (End-User Licence Agreement) since I have heard there are quite strict guidelines where distribution is concerned. After all, if all you want to do is have a better knowledge of C++ and of how HPB_Bot works, I should not see why you do not download it.