I thought I would check (using Command F) just for the educational aspect but could not see, given the apparent options, how I would add system files to the search.
1. In Finder, type Command-F. A Finder search window opens. Enter your search term(s).
2. Click the plus sign at the right side of the window to add another search condition.
3. Click on
Kind, and choose
Other… from the pop-up menu. A sheet descends with a long alphabetical list of attributes.
4. Scroll down to
System files and select it. It's not a bad idea to check the
In Menu checkbox while you're at it; this will save having to invoke the
Other… sheet in any future case that you want to include System files in your search.
5. Click OK, then click on
don't include and choose
include from the pop-up menu (that's assuming Snow Leopard engages in the same counterintuitive practice as Leopard of assuming that though you've just included the System files attribute you don't want to make use of it).