There are a couple of web sites that allows you to create your very own customized search engine that is only limited to searching on specific sites.

Check out Rollyo, which gives you this ability by specifying up to 25 web sites that the search will only be performed on them (I think it's 25, anyhow).

You can also take a look at Google Co-op which does the same as Rollyo as well as Yahoo Search Builder.

All of these sites basically do the same thing, which is to create your own personalized search engine. They have minor differences in configurations (some allows more sites to be search in one search engines, some allow less), but they will produce something that will probably answer your needs (I hope).