Logging in to clear up some common misconceptions...
Whather or not your CPU is 64-bit has no bearing on the full-screen display of DOS programs in Windows. If you can run
any DOS programs, then you are running a 32-bit version of Windows.
Both Windows XP and Vista 32-bit can display full-screen DOS programs, with graphics, no matter what CPU or graphics card you have. The trick is all in the software.
For Windows XP, the solution is this:
http://www.phatcode.net/downloads.php?id=196Long story short, recent NVidia and ATI drivers bork DOS graphics modes. This fixes them. Reboot in safe mode, extract all files in the ZIP to a temp directory and run install.bat. Then restart, and you should have your full-screen DOS graphics back. If you ever update your graphics driver, you will have to do the patch again.
For Windows Vista, you have to use XP graphics drivers, because WDDM (Vista) drivers disable int 10h. This disables Aero, however.