How to make sub-sites searchable from the main blog in MS

Hi could you tell me the best way to make all my sub-sites searchable and index-able from the home site? I'd like people to come to my home site and find a directory of all the sub-sites. In addition, I'd also like them to be able to do a network wide search from the home site in all sub-sites for a particular item they may be looking for. It's kind of a shopping directory. Thanks!