Microsoft’s SuperPreview, released as a beta last week, looked promising but in practice fell short in several key areas. The biggest problem is that although SuperPreview can snapshot a page in IE6 or any other browser, it’s just that: a snapshot. Layout bugs are just the beginning of IE6′s problems – it also falls short in both Javascript and CSS capabilities, which may not be evident in a screenshot. Furthermore, SuperPreview will eventually be a part of Expression Web 3, which is not free.

Microsoft does provide free virtual machines with IE6 pre-installed, which gives us the interactivity we need. Although bulky, they have been the best solution available to web developers for testing legacy versions of Internet Explorer. However, this still doesn’t help with Firefox, Safari, Opera, or Chrome.

Enter Xenocode’s Browser Sandbox. It leverages Xenocode’s Virtual Application System, which packages existing Windows applications into small virtual machines, so that they require no installation or configuration. Xenocode has created packages for the modern web browsers available to Windows users: Internet Explorer 6, 7 and 8, Firefox 2 and 3, Opera, Chrome, and Safari – and they’re all free.

The end result is that you can download each of the 8 packs from the Xenocode site and store them together in a folder or flash drive. Then whenever you want to test a site in Internet Explorer 6, you just run the ie6.exe file and you’ve got a fully functional version of IE6 running, with no installation or footprint. The same goes for Firefox, Opera, Safari, and Chrome. The files range in size from 5MB – 40MB, depending on the size of the browser itself. All 8 will easily fit on a 250MB thumb drive.

I’ve been testing them today, and so far the experience is great. The only complaint I have so far is that the IE Developer Toolbar isn’t included in the Internet Explorer packs, which I’ve come to depend on for debugging IE6.

The Browser Sandbox website does leave a bit to be desired in terms of instructions. To download a browser pack, simply click on the green power button icon in its panel. Here’s a screenshot:

Note: If you don’t see the green buttons wait for the page to fully load. In my experience they were the last thing on the page to load.

The 8 browser packs available on the Xenocode site are free, but if you want to make packs for other browsers, such as the Firefox 3.5 beta, you’ll need to purchase the Virtual Application System from Xenocode for $40. With it you can actually package any Windows app – they’ve done so with GIMP and Winamp as examples.

Only Windows is currently supported, although the company’s website promises they are working on support for Mac users (no word on Linux).