It already exists!!

Ok, so this is the product I've been looking for. Little did I know, it's already here.
It's a tablet PC made by a company called Paceblade from the netherlands. The Slimbook d220 has a screen that works via digitizer pen (active digitizer/mad accurate drawing/pressure sensitive for line weight) or a resistance digitizer (like my Treo/general touch input with any object). So far, my only complaint with it is the screen's resolution - It's XGA which means 1024x768. These days, I'd expect a much better resolution - at least WXGA. That being said, it's a 12.1" screen, which is pretty small, so that is probably a pretty comfortable resolution.
The biggest downside - it's $4,000usd.

From the PDF Brochure :
"The new SlimBook 200 series is the next generation of our successful
slimbook line. The three innovative models of the SlimBook 200 series are
designed to enhance productivity for mobile professionals by offering a
computing solution that functions in the field as well as on the desk.
The SlimBook 200 series combines the power of Intel Mobile Core Duo
Technology with the new Microsoft Windows Vista Ultimate operating system
in a sleek lightweight form factor that can be carried about as easily as a pad
of paper, but features the full functionality of a top-of-the-line PC . It represents
the fastest Slate Tablet PC on the market today.
The SlimBook 200 series offers a 12.1” LCD dual mode screen that switches
between active digitizer (pen) and touch screen input. This technology was first
introduced to the market by PaceBlade years ago on its famous PaceBook
series. Additional features include four user-programmable buttons, biometric
fingerprint reader, Bluetooth and wi-fi connectivity, eSATA support, a Type II
PCMCIA slot for expansion possibilities and Harddrives that starts at 160GB.
Powerful Mobility
The PaceBlade SlimBook 200 series are state-of-the-art Tablet PCs designed
for mobile professionals and are known for their attractive, lightweight design
and large 12-inch ‘Wide Angle View” display with 160° viewing angle.
The SimBook supports instant screen rotation that provides the possibility to
switch so that you can switch from portrait to landscape mode without
restarting your computer.
The SlimBook 200 series is powered by Intel Core Duo or Intel Celeron
Mobile Technology processor for ultimate speed and processing efficiency.
Resistive Touch Function
The PaceBlade SlimBook 200 series is supported by a wide range of
accessories to create the ultimate configuration and usage, for instance our
grab-and-go docking station for quick mobility. For travelling purposes we
provide extra batteries, Car & Truck adapters or special bags, like ruggedized
bags, these are all supported products at PaceBlade.
PaceBlade Tablet PC features
The PaceBlade 200 series is supported with a wide range of accessories to
create the ultimate configuration for the user, like a grab-and-go docking
station for quick mobility. Extra batteries, Car & Truck adapters or special
bags, like ruggedized bags, are supported products at PaceBlade."

Get it from The Tablet Store: