If you are looking for a Google(tm)-like capability to search your local PC hard-drive, I know of three products - Google Desktop, Yahoo Desktop, MSN Desktop and X1. Each has its own set of strengths and weaknesses you should investigate before making a decision.
In short, each product works pretty much the same way - you install an application on your PC, once installed the application does an initial indexing of your files, and thereafter you can use some kind of search interface to find files on your PC.
Some differences exist in the options for your search (only file of a certain document type, only files within a certain date range, etc.). X1 is the only one that is a commercial (you have to pay for it) product - the others are free. They also differ in if/how they search your email folders (and any attachments to those emails) along with the files on your hard-drive. These can be big differences so it is prudent to try each product before making a big commitment.
X1 is also different in that it can be used as part of an intranet/enterprise search solution - sort of like having your own Google appliance at your business. It also comes with an SDK for businesses to build their own search solutions. Google has something similar for their Google Appliance. Yahoo and MSN don't offer enterprise solutions to complement the consumer products.
There have also been plenty of articles in the press about how these products do (or do not) report information back to the businesses that offer them. This is not my area of expertise but my understanding is that Yahoo, Google and MSN all send information back. Each has made claims about how that is only information that is about how the searches are working and not the contents but that is, to my knowledge, unsubstantiated. I've read that the latest Google Desktop has options for you to turn this off. X1 is different than the others in this regard - it may share with your enterprise X1 server (if used) but I don't believe it is known to report anything back to X1 if you are just a single stand-alone user.
None of these products generates a documented export file that is an index of what is on your disk - something that could be used by another application. So, if you wanted to create an index that could be incorporated into a local database application or something like that, that probably won't work. Each expects you to use their own PC client application to do the searches. In the case of Google Desktop and Yahoo Desktop, they both look pretty much like the web interfaces which is a plus for most people. X1 works more like a super-charged version of the Windows File Explorer or some of the file management tools (remember Magellan?) that were available in the last days of DOS.
You can lean more about each of these products by visiting the website for Google Desktop, Yahoo Desktop, MSN Desktop, or X1.