We use FileSearchEX around here. It is really cheap ($30 plus $5 per user of the software) and works very much better than the built-in indexing for content searches.
I plan to look into the Windows Grep solutions linked in this thread for myself and the other tech, but I am not sure these would be user friendly enough for our primary users who needed this functionality.
I haven't tried searching system files but searching for excel and word docs across a mapped drive is a nightmare in Windows 7. As the solution we use This, it's called FilesearchEx
AFAIK the search ability depends on the version of doc format used. Also, the Windows 7 search function kind of sucks anyway.
At work we use FileSearchEX. Give it a try. If you like it, a licenses is really cheap.
As an admin I loved the classic file search tool Windows 2000 had. It assumed that you knew how to use wildcards and knew what an extension was. For example, I could easily search my entire hard disk for a PDF file (*.pdf) that has the word "VMware" in it. It didn't use indexing and it was quick.
Windows XP has this capability if you tweaked the search settings and got rid of the goddamn dog. But Win2K had the non-fluffy interface with all the capability.
From the looks of your utility it seems you and I are on the same page. I cant wait to try it.
One thing that Win2K/XP was missing was the ability to filter by all three date Fields Windows uses (modified, created, and accessed) - that would be cool :)