As any Windows web developer knows, cross-browser compatibility can be a real nightmare to test without a Mac handy. Hopefully the release of Swift will make things a little easier.
You can download the current alpha release from the website; although the last time I checked, the download seemed to be unavailable. This is probably due to bandwidth limits being exceeded - I notice Ann van Kesteren has just linked to the site and Vitamin linked there earlier (which is how I discovered it myself).
Here’s a nice screeny of it running on my Windows 2000 Pro machine at work: