To determine which SharePoint 2010 Products are installed for the purpose of inventory or conditional code logic, you can interrogate the registry.
The screenshot below illustrates the keys that need to be evaluated.
The following table shows a GUID to SKU mapping that can be used to determine which products and SKUs are installed.
|BEED1F75-C398-4447-AEF1-E66E1F0DF91E||SharePoint Foundation 2010|
|1328E89E-7EC8-4F7E-809E-7E945796E511||Search Server Express 2010|
|B2C0B444-3914-4ACB-A0B8-7CF50A8F7AA0||SharePoint Server 2010 Standard Trial|
|3FDFBCC8-B3E4-4482-91FA-122C6432805C||SharePoint Server 2010 Standard|
|88BED06D-8C6B-4E62-AB01-546D6005FE97||SharePoint Server 2010 Enterprise Trial|
|D5595F62-449B-4061-B0B2-0CBAD410BB51||SharePoint Server 2010 Enterprise|
|BC4C1C97-9013-4033-A0DD-9DC9E6D6C887||Search Server 2010 Trial|
|08460AA2-A176-442C-BDCA-26928704D80B||Search Server 2010|
|84902853-59F6-4B20-BC7C-DE4F419FEFAD||Project Server 2010 Trial|
|ED21638F-97FF-4A65-AD9B-6889B93065E2||Project Server 2010|
|926E4E17-087B-47D1-8BD7-91A394BC6196||Office Web Companions 2010|
In the screenshot above you can see that I have SharePoint Foundation 2010 and SharePoint Server 2010 Enterprise installed. If you have SharePoint Server installed you should always see SharePoint Foundation as well. SharePoint Foundation is the free version of SharePoint meant for small department implementations or as the foundation for other applications built on top of it. This means it is possible to see Foundation without server.