I'd go one further than the article takes it. If your intention for doing this is because you're running out of space on your primary harddrive, then, it'd better to move the non-program essential files to an external harddrive (ex: mp3's, pictures, documents, etc) and only use the C:\ as a drive to install and run programs from. Not only should this make the computer faster, as its not accessing files for the programs from the same drive as its also trying to run the program from, it also makes it easier to salvage your data in event of a system crash... as the only thing that you'd lose would be the install of the operating system and the programs installed, which you should have the original on cd/dvd or be able to redownload again.
With today's harddrives being so large, and laptops easily coming with 80gb harddrives as a minimum standard now, you should never run out of storage space for programs. I have over 50 programs installed on my computer and am barely over 15GB's, including the operating system.
If you are running out of C:\ space, just buy an external drive, copy all your data to it, and that should free up space on your c:\ also allowing more space for the operating system to use as virtual ram.

If your intentions to do this are to move programs from one computer to another, w/out having to install the program on both computers, you could 'thin'-stall it. I suggest this program. http://portableapps.com/ that will allow you to install a program to a usb key and move it from computer to computer w/out having to install it on each computer.

I do it all the time. I put all my most useful programs on a flash drive and carry it with me. CCleaner is one of them. A lot of the time you don't even need a portable version of the software to run it from an external memory device.

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Slax, BartPE, Knoppix, even the latest versions of Suse come with a utility for making your own custom boot image that can be installed on a pen drive, and they all work great. I have an 8 GB pen drive that has its own boot menu that allows a boot to all 9 XP cd images, a few vista images, gparted, ghost, partition magic, knoppix, easy recovery, spinrite, and a few other good tools. It saves me from having to lug a wallet full of CD's to client sites. This is a great idea, but I suspect the Q that led to the post was someone wanting to use software illegally this way.