On www.sccmexpert.com, they have recently posted an update to the Individual MOF collection which was originally for SMS2003. They've been updated to be ConfigMgr - friendly. Go there, click on "The Mof", Mof Tools, then "Get the Scripts" (note; you may have to sign up on their web site--but it's quick & free). Then grab "ConfigMgr MOF Snippets".
With SMS 2003 (and earlier), extending hardware inventory has been essentially the same; you add specifically crafted text to sms_def.mof on the server, and if data objects were needed, you "mofcomp'd" those data object text files on your clients. With ConfigMgr 2007, it is just different enough to possibly be a little confusing. I'll try to clear up any confusion.
In ConfigMgr 07, on the server in inboxes\clifiles.src\hinv, there are two mof files: sms_def.mof and configuration.mof
You can of course leave them alone, but if you've 'extended hardware inventory' with SMS2003, or you've heard of doing this and want to do so, in a nutshell, in sms_def.mof if you were to add specifically crafted text to the bottom-- specifically the bits that make up the "Report" section, (the section with TRUE or FALSE in them), that would update the Hardware Inventory policy which your MPs offer to clients. Once the clients pick up that from the MP, their next Hardware Inventory they'll try to report.
In configuration.mof at the bottom, you would add the bits that make up the "data" section. I like to think of it as "telling the client how to report on what the policy is asking for". For example, the Hardware Inventory policy may ask for McAfee AntiVirus information, because you just added that snippet to the bottom of sms_def.mof. But a client won't know "how" to report on that custom data without instructions. Configuration.mof is where you tell the client to pull that information from 'these specific registry keys'.
If you're just starting out with ConfigMgr, you can ignore these next 2 pieces of information... If you're a SMS2003 admin, just a couple things to help clear things up. #1) Mofcomp. Forget about it. You know what I'm talking about! Configuration.mof does all the work for you. #2) In the snippets, you may notice a decided lack of a line you were used to seeing in the mof snippets for SMS2003, the #pragma namespace lines. Since sms_def.mof is now only for cimv2/sms namespace, and configuration.mof is only for the cimv2 namespace, those lines to tell the mof "The next section is for this namespace" are just redundant and not needed.