Seriously listen to these guys and do not mess around with 16 bit asm + dos. If you want to start simple pick up a AVR 8bit chip. There is also PIC but pic uses a banked/paged memory system on a lot of their chips which makes things dumb. With AVR 8 bit you have about 130 instructions or so and properly aligned memory that is not split off into chunks. After you get bored with that which you probably won't go an move to ARM.
I started with PIC but after getting tired of all the bank switch and crap I moved to AVR and it is much nicer to work with at the asm level. Eventually I plan to move to ARM and mess about there at some point maybe.
I use bare avr chips not the arduino platform because arduino makes it a nasty hack to do any asm with it.
The only issue with working with the micro controllers is to really do anything interesting you are going to have to learn some electronics. I found this the most difficult part is the actual electronics not writing of the firmware which even in asm is relatively easy.
Right now I am working on a sound activated trigger switch using a AVR and a Microphone. Still trying to understand the electronics behind it already understand the firmware part.