Keep your computer clean with virtualization
I like to keep my computer as clean as possible. I find that after about two years of usage, I accumulate many applications for which I cannot find a use anymore. Some I use very rarely, not nearly enough to warrant their encroachment. I have always found it surprising when I find programs whose purpose I do not even remember.
I have known about VMware for a long time, but have not paid a lot of attention to it. In short, VMware is able create virtual computers. That sounds fancy, and it is. VMware is able to simulate computers. Through it, you are able to operate the virtual computers much like you would operate you own, real machine. You can power off, power on, add hardware, insert floppy disks, optical and USB media. And the nice thing is that each virtual machine you create is run as any other program by your operating system.
The first thing I suggest you do is separate your computer habits into categories. Myself, I used very broad categories; entertainment and software development. I decided to use my host (as in the real, the box in front of you) computer for entertainment, because of Windows 7's ease of use and software library (no, they did not pay me). I decided upon Debian Linux for the guest computer (the virtual machine) for my development. This created the need for only one virtual machine (VMware supports multiple).
The natural choice was VMware Player, which is their non-commercial freeware version of the software. VMware stores each virtual machine as a large file (with the option of using many, smaller files instead) on the hard drive partitions known to your host. What happens in the VM stays in the VM. Go ahead and install whatever software you wish on the guest computer. Nothing will leave the large file. Being a simple file, it can be transported between computers, so you can take your virtual machine wherever you go.
The guest can be configured in great detail. You can set the amount of RAM, hard disk space, and a number of other peripherals. You also have the option of letting VMware install a guest operating system as well. You will need the installation disks (CD or DVD), just like you would for a regular computer. If you would rather do everything manually, you will simply get a virtual machine that is completely empty, and will have to deal with booting your OS installer yourself. The optical drive of the guest can be connected directly to the optical drive of the host. However, the easiest by far is to use an ISO disk image, which will seem like an inserted CD or DVD to the guest.
One of the noteworthy features of the virtual machine is power suspension. When I am done working inside the guest, I can choose to suspend power to the virtual machine, akin to closing a laptop, or putting it to sleep. The benefit of this is that when you have a few tens of windows spanning multiple desktops, the next time you start the guest, everything will be where you left it.
Virtual machines can also be a great way to experiment with unfamiliar operating systems. First of all, it saves space. You will not need to bother with a second computer, or with partitioning your hard disk or with multi-booting. Everything is just a large file on your host partition, remember? Try out Linux if you have not yet. Or perhaps DOS 6.22 along with the older versions of Windows, such as 3.11 if you want a challenge.
Want to get fancy? Install Snow Leopard or some other Mac OS, and then take your Windows 7-based laptop to a Starbucks and finally be able to fit in. Just remember that a Tall coffee is not what it sounds.
Once you manage to get Linux working on your guest, you may want to use it for riskier web surfing, due to the known imperviousness of Unix/Linux operating systems to common viruses and trojans found online. You can do your banking using the guest. Or perhaps use eBay, along with PayPal, or any other websites where personal information along with credit card information is necessary. You will probably be just a bit safer than on a Windows environment.
Have fun experimenting with virtualization!