The 900HA looks to have the same Atom processor and 8.9", 1024x600 display as the Eee PC 901, but it includes a 160GB hard drive instead of the latter's 12-20GB of flash storage. With a gig of RAM, a four-cell battery, and a copy of Windows XP Home Edition, the 900HA costs $350 with free shipping (although it's only up for pre-order right now).
That makes the 900HA considerably cheaper than the Eee PC 901, which still costs almost $500 according to our price search engine. $350 also happens to be the exact price of the Celeron-powered Eee PC 900. Both the 900HA and the 900 have four-cell batteries, however, whereas the 901 has a six-cell unit rated for up to 7.8 hours of run-time. The skimpier battery and potentially power-hungrier storage could make the 900HA less mobile, but some may prefer the increased capacity and higher performance of the mechanical hard drive.