Here is a very valid low-cost alternative to the Sony UX series micro PC or Samsung Q1 UMPC, the Raon Vega Windows XP PDA.

The Raon Vega is actually claims for itself to be the smallest Windows XP portable PC with measurements of 160 x 80 x 27.5mm.

Features of the Raon Vega include a 4.3 inch touch screen with 840x480px resolution, AMD Geode LX800 500 MHz CPU, 30GB HDD and 512MB RAM.

Dynamism sells the RAON Vega for $879.00.
The Wi-fi connectivity is achieved with a bundled USB stick. The battery life of the Vega Windows XP PC is 5.5 hours. See also the Raon Vega product page.

Considering that the Sony UX180P sells for $1,799, the Vega is a real bargain at half the price. If you like the UMPC concept the Samsung Q1 is in the same price range as the Vega.