Ddie asked the Windows forum about setting up a second Windows installation for testing purposes without buying a second PC.
There are several ways to set up a second Windows environment on your primary computer. But let me start with one that doesn't work: You can't install Windows on an external drive and boot from that. Windows only works from an internal drive.
But here are a few things you can do:
Set up a dual boot: You can install another copy of Windows on a separate partition or a second hard drive. When you boot, a menu will ask you which installation to load.
The downside: You have to either buy another hard drive or give up room on your current one. Also, you'll have to buy another copy of Windows.
For instructions, see Dual-Boot with Windows 7.
Create a software PC. A virtual machine (VM) is basically a fake computer, created by software, running inside a real computer.
I can recommend either of two free programs for this job. VMware Player is the easier one to set up and use.
VirtualBox, while a bit harder to figure out, can do things that VMware Player can't. For instance, it can save snapshots of your VM so you can easily return to what it was last Wednesday or last year.
Although the programs are free, using them won't be. As with the dual boot option, you'll have to buy another copy of Windows.
Use a free, virtual version of XP. If you're running either the Business or Ultimate edition of Windows 7, you've already bought a copy of XP for running in a VM. All you need do is download and install Windows XP Mode with Virtual PC.
Do your testing in a sandbox. Rather than use a whole Windows installation (and buying another copy of Windows), you can test software in a sandbox--an environment within Windows that prevents what's going on inside the box from changing what's outside.
For instance, if a program in a sandbox changes the Registry, those changes don't exist outside the sandbox.
The best program I know for this job is Sandboxie. With it you can create and run multiple sandboxes, launch any program in any one of them, and control what happens to the files you download, save, or create in a sandbox.
But is isn't free. A one-year license costs €13 (about $16 as I write this). A permanent license costs €29 (approximately $26). That's a lot cheaper than a new copy of Windows.
Read the original forum discussion.
Contributing Editor Lincoln Spector writes about technology and cinema. Email your tech questions to him at email@example.com, or post them to a community of helpful folks on the PCW Answer Line forum. Follow Lincoln on Twitter, or subscribe to the Answer Line newsletter, e-mailed weekly.