<p>I've been adding css support for <strong>handheld</strong> to my website but haven't been able to find a good tool for testing. </p>

<p>I tried using the webdeveloper plugin for Firefox but it doesn't work for me. Maybe that is because all my css is in the html and not a seperate css file.</p>

<p>Are there any other testing tools available aside from going out and buying a handheld device?</p>

If you have Visual Studio, there should be device emulators which let you test mobile IE, or they can be found standalone on Microsoft's site.
Here are some for WM 5
.  There is an
OpenWave simulator
available to test that browser.
Blackberry simulators
are available as well, to test the Blackberry browser.  You can (kind of) test iPhone support with Safari, although you can't verify the viewport meta-tag.  There's an
Opera Mini simulator
here.
Also, get your CSS out of your HTML :)