Hi samers94
Yes, you can use a VM. I use VMWare Fusion v3.0.0 and here's how to do it. Thanks goes to Zef for originally showing me how to do this.
Make a new folder on the desktop named themetest and then add in to it Chameleon's cdboot file, a new folder named Extra then inside the Extra folder, make a new folder named Themes.
In the Themes folder add the Theme folder containing your new theme, and you also need to add the Default theme, which is needed or else when running this you'll only see the famous EBIOS read error: Device timeout error instead of your lovely theme.

Open TextEdit, or another text editor on your Mac, copy and paste the following in to it and save it with a name of org.chameleon.Boot.plist (this was formerly com.apple.Boot.plist). Add the
Theme key/string to point Chameleon to your new theme and then save it in to the Extra folder. Note: in this file, the name of the theme is to be the name of the theme folder containing the theme you want to test.
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Timeout</key>
<string>5</string>
<key>Theme</key>
<string>Blackosx_Switch_Theme</string>
</dict>
</plist>
Your folder will look like this:
UPDATE: The use of com.apple.Boot.plist is now deprecated and org.chameleon.Boot.plist is now used.
Then in terminal, cd to the desktop and run a command to make your themetest folder in to a bootable .iso.
cd ~/Desktop
sudo hdiutil makehybrid -o themetest.iso themetest/ -iso -hfs -joliet -eltorito-boot themetest/cdboot -no-emul-boot -hfs-volume-name "THEME_TEST" -joliet-volume-name "THEME_TEST"
You'll end up with a themetest.iso on your desktop which you can open in a VM.
From within WMWare Fusion, I use the following steps:
• Create a new virtual machine
• Click 'continue without disc'
• Click 'use operating system installation disc image file', and select the themetest.iso
• Continue
• Choose operating system - leave at default which is Linux / Ubuntu
• Click Continue and Finish
• Give it a name or just accept the default
• And voila!.. Chameleon

You can now use this to test positioning and placement of images, the menu and the bootprompt. Though sadly you won't be able to see all devices icons for different drives as VMWare only thinks you have a cdrom attached and hence Chameleon will only show your device_cdrom graphic and the device_selection graphic.