Sorta getting off topic, so let's try this....
Depending on your computer the only way to get into DOS is to either select "command prompt" from your accessories menu, or to have it boot in safe mode to command prompt. The only problem with this is that it isn't really DOS, just a "window" into DOS. The reason it won't let you move around freely and denies you access to a lot of things is because those things are being utilized by Windows which is still running. Wouldn't want you to try to delete something it's using, now.
The easiest way to use DOS is to create a floppy (anyone still have one?) or maybe a burned CD that will boot your system directly to DOS without loading windows. Then get into your system setup (usually by hitting DEL at initial boot screen) and change your boot order to have whichever drive (floppy or CD) as a first check, before going on to your hard drive. This will allow you to get in DOS unfettered by Windows.
The DOS boot disc is very useful for two reason:
1. You have a virus or spyware program that your software can identify, but can't delete because it's "in use" or has "access denied." It auto-runs when windows boot and you can't delete it while windows is up. Although HijackThis is a great program for getting rid of these, sometimes you just need to find it's location, go into DOS and delete it.
2. Sometimes your system will get so screwed up that you can't get windows to even boot. Not even in safe mode! (Blue Screen of Death) Sometimes you're only option is to reformat your hard drive and reinstall windows. But what about that thesis paper you've spent the last 6 months on? That big report for work? The high scores file for your mame? With a DOS boot disc, you can get into your file structure, copy your files to writeable media, and have them ready to put back once your format is complete.
Sometimes it helps to remember how to use these things long before Windows came out.