To qualify as a UMPC the device must meet the following hardware specifications:

• OS: Windows XP Tablet PC Edition 2005 (will incorporate Windows Vista when it is released).
  
• Display: Screen size: 7 inches or smaller (future models may vary); Screen resolution(s): minimum 800x480 resolution with 800x600 and 1024x600 available through video scaling technology; the display must be a touch screen, not a Tablet PC-style touch screen.
  
• Weight: less than 2 lbs.
  
• Input methods: touch screen / stylus; buttons to navigate/select menu items; must be capable of accepting optional Bluetooth or USB cabled external keyboards; uses Touch Pack software for bigger, finger-friendly icons and buttons for launching applications, playing media, and navigating; uses DialKey QWERTY-based thumb keyboard.
  
• Connectivity: incorporates Wi-Fi, Bluetooth, and Ethernet port.
  
• Processor: Intel Celeron M, Intel Pentium M, or VIA C7-M.
  
• Storage: 30 GB or greater hard drive.
  
• Some devices may include additional built-in features such as GPS, a Webcam, fingerprint reader, digital TV tuners, and CompactFlash and SD card readers.

The key elements differentiating Microsoft's UMPC from other Tablet PCs seem to be the touch screen and the screen size of 7 inches or smaller.

Source

Microsoft Website

Thanks for the link

hmmm, explains a lot... I assume this to be a BIGGER PDA only... with lotsa features as a PC... less in hardware