Try configuring a Dell with a 64GB solid state drive, a Core 2 Duo or equivalent (not an Atom) processor, under 5 lbs. The only option from Dell is the Latitude 13.
For about the same price as the Macbook Air, you get Intel integrated graphics; a battery that PC World rated among the worst, at about 3.5 hours; 802.11g (vs. n on the Macbook); no multi-touch trackpad; and an extra pound and a half of weight.
Brand new Samsung 64 gig SSD $150 at Newegg.com.
Have you looked at brands other than Dell?
And the K325 is equivalent to the 1.4 GHz Core2 Duo in the Macbook Air (per the independent CPU testing I referenced above). And it's under 4 pounds - 3.2 pounds to be exact. So the penalty is 12 ounces for 5X the storage, and half the price.
Battery ratings? Anandtech independently tested the battery and found it rather "optimistic" at 5 hours. In fact, it came in at about 2:45, about the same as the Dell when running xVID playback and heavy web browsing. No surprise given the equivalent CPU capability, graphics capability, and bigger battery in the Dell unit (the SSD does save power, but the battery is a lot smaller).
Not to mention you can pop out that battery in the Dell and keep going. A bit hard to swap batteries on the Air; if it runs out, better plug it in, no option to pop in another battery and keep going!
And the Inspiron 101z has 802.11n as well, and a multi-touch trackpad. Oh, and it has a 1.3 MP webcam as well... Yes, it weighs 12 ounces more. Of course, it's also half the price.
So the real choice is: are you willing to pay $1000 for a 2.3 pound, 64 GB computer with 2GB of RAM, or do you want to pay $500 for a 3.2 pound, 320 GB computer with 4 GB or RAM (expandable to 8 GB)? Everything else - network speed, CPU speed, display - are the same. Except, of course, external connectivity. The cheaper device has more USB ports and a wired Ethernet jack as well, and also includes dedicated HDMI and VGA ports, no special adapter cable required.
How much is that 12 ounce savings worth to you?