If we accept that it's OK to try to run the full Windows 7 operating system on these weak hardware specs, the MacBook Air is also capable -- in fact, arguably more capable than the HP Slate 500. Both have 2GB of RAM, and 64GB of solid state flash storage, but the MacBook Air has a dual-core processor.
Edge: Tie (virtually equal -- depends on whether a tablet form factor or a full physical keyboard are more important to you)
The HP Slate 500 is also $200 less than the base 64GB model of the 11.6-inch MacBook Air. It seems that the HP Slate 500 has a slight edge as a mobile business platform capable of running Windows 7.
There are a variety of other considerations to weigh between these two, as well as the fact that there are remote desktop solutions that enable other tablet platforms to work with Windows software as well. Ultimately, the decision is subjective and personal, so make up your own mind. As far as I am concerned, I love Windows 7, but it is not an OS I want on a tablet.