When I started on the internet, it was common knowledge NOT to teach someone--who strongly desires the knowledge--how to hack another computer. Mainly because of their intentions and hidden agendas. Most people who really hack don't do serious damage to other computers, they just gather information, and of course, utilize it as some sort of defense mechanism (if you are that into the shit). I will leave you with a few pointers...
Forget about DOS, that shit is older than dirt. Microsoft doesn't even code their operating systems with it anymore, so they claim. If you want to learn how to break into another system, then install some sort of unix/linux platform (I use FreeBSD, I highly recomend it to you). I would suggest buying a book on it as well, but the best way to learn is hands on, with a small command reference sheet. Don't install it as a work station, though. Buy another computer, it doesn't have to be a good one, just a hundred dollar 386 with a NIC card will be just fine.
Go study the "art" of exploitation and system vulnerability. Real hacking is not done through remote system administration, but by finding holes in another system. Scan a broad range of IP addresses for specific exploits, then study how and why they were created. Now the true, and I mean REAL hackers hardley do any of this, they learn the C/C++ language (highly used in coding the most popular computer software) and code/create the vulnerabilities themselves.
When I was younger, I had a huge thirst for hacking. I didn't want to read or learn anything. I wanted someone to slap a manual on my lap telling me exactly how to break into any system I wanted, but thats not the way it works. The best thing for you is to READ. Then READ some more until your eyes bleed.
LEARN:
Unix/Linux operating systems.
Networking (including the 7 layer OSI model), TCP/IP and the way computers talk to one another.
C/C++ is an option, not taken by many, but more useful then anyone will believe.
Just to get started...
Now of course im going to tell you that, I don't hack computers. This is just common knowledge that I have picked up over years of computing. Do with it as you wish, but the chances are that, like most, you are going to be turned away by the extensive amount of readying, studying, and research that is required.
Good luck.