Microsoft products license keys using WMI

I've been searching in vain for a WMI script(s) that will allow me to retrieve the product license keys used for Microsoft products installed on a machine (e.g. xxxxx-xxxxx-xxxxx-xxxx-xxxxx). This includes the likes of products such as Sharepoint, SQL Server and Exchange but all I seem to be able to find are scripts to retrieve the actual Windows license key.

What I've tried thus far (has to be WMI so no powerscript please):

1. Tried win32_product class but the fields I'm interested in (productid) does not exist on windows2003 and I have a mix (30% to 70%) windows 2008 vs windows 2003 servers
2. Tried going to the registry but the there is no standardized location for product keys and the resulting solution would be really "nasty", but if its the only way I will have to consider getting down and dirty

Reason for this: I have to go through a multitude (> 200 machines) and list the licenses used for the mentioned Microsoft products on each of the machines for auditing purposes.

Any help would be greatly appreciated even resources that will point me in the right direction. Alternatively, if Microsoft has a product capable of doing this, I'd be interested in that as well, but first prize would be a WMI script.

@Lizz, had the most helpful contribution and just confirmed my fears that if I want to get this done, it will involve manually searching various place in the registry for each flavour of Microsoft product.

So what I will do is use the tool she mentioned and monitor the registry sections it accesses. I will then incorporate that along with the URL she supplied for Sharepoint and go through the various locations the keys might be stored. Dirty, but it will work