First of all you'll need an avatar account go here to create one.
Next you'll need a viewer. At this time our InWorldz viewer is undergoing builds and testing. You can use any viewer out there
for now including the LL viewer. I recommend the hippo which you can get here.
Now you'll need to add some argument strings in the properties shortcut tab for your viewer shortcut.
It should look something like this in the target line : "C:\Program Files\Hippo_OpenSim_Viewer\Hippo_OpenSim_Viewer.exe" -loginuri
http://inworldz.com:8002/ -helperuri
http://inworldz.com/Login and voila, welcome InWorldz!