There aren't any simple and easy IFilter templates as far as I know, but there are some pretty detailed instructions (including pseudo-code). You can find one example here:
http://msdn.microsoft.com/library/default.asp url=/library/en-us/odc_SP2003_ta/html/ODC_HowToWriteaFilter.asp frame=true
In what kind of database are you storing the files you are hoping to index Depending on your data store, you may also need to implement a protocol handler. In simple terms, a protocol handler understands and follows the rules of the data store that contains the files that need to be indexed.
Let's use the Windows file system as an example. Let's say you need to be able to index a new file type called .foo and that file type will be stored in a Windows file system. Well, first you'd need to write an IFilter that's capable of understanding the content of .foo and passing it to some kind of index. In addition, you'd need some way to get to files of type .foo. Since they're stored in a Windows file system you'd need something that could understand and navigate that file system for the IFilter so that it could index the files you want to be able to search. This is what your protocol handler does.
Of course, the above is an oversimplified explanation of a protocol handler. It should also be noted that the Windows file system protocol handler is included with the software. Still, you get the general idea. If you need to index files in a database or file system for which a protocol handler does not already exist, you will need to write one. You can find additional information about protocol handlers here:
Paul Nystrom - MSFT