Resizing the window manually is one approach, but you can never quite get to the exact size you want to test for.
One handy tool for testing is the "web developer toolbar" for firefox. one of the menu options it gives you is resizing the browser window to a specified size.... and you can add your own sizes to the menu.
SOME of the functionality in the toolbar, like "document size" are broken in anything newer than FF 3.5.x, however the 'resize' menu still works just fine. Just go into "resize -> edit resize dimensions" and type in the ones you want to test for.... they'll appear on that same "resize" menu item from that point on.
With the capabilities of most of the handhelds increasing at a blazing pace, I've been going three target sizes on media queries:
Single column for <768px
Dual column for 768... 1104px
triple column (if there's enough content) at 1104..1232
Always working in fluid/semi-fluid layouts.
Your current page going through it I'm not seeing there's enough content there to even bother with two sizes, much less three -- though the hard to read script fonts and low color contrasts aren't helping matters a whole lot either -- no matter how 'pretty' they are.
The nonsensical use of a H2 and wrapping div around the h1/h2 pairing not helping matters a whole lot either... nor the comment placements that could be (ok, ARE) tripping IE and FF rendering errors.