Which will you use more often? Lion or Windows?
I haven't fiddled with installing a Mac operating system on a PC for years, but it used to be such a pain. It may have gotten a little bit easier, but imaginably it's still an annoying process (especially keeping it updated). As ^MacDawg said, installing Windows on a Mac is easy as cake (I use VirtualBox for virtualizing; it's free).
$1500 is a pretty decent budget, but you're limited to either the 13in MacBook Pro or 13in Macbook Air. What else will you be doing with the laptop?
I love the the MacBook Air, so I'd recommend that (SSD, higher resolution screen, ultraportable). But depending on what you need it for, you may need the expansion aspects of the MacBook Pro (have more than 4GB RAM, need more than 256GB hard drive space, desire for extra ports, etc.)