Copernic Desktop Search - The Search Engine for Your PC
This has gotten some good reviews. It covers a lot of file types, and one can specify the location of the index files (you don't want to back these up, so they should be stored in a folder that's excluded from backup).
It does not index Eudora data - only Outlook. I can't tell if it supports indexing of a network drive, probably not.
Yahoo is partnering with X1. At the moment X1 and Copernic may be in the lead, with MSN next and Google lagging. Google has to get in gear.
I'll probably opt for X1/Yahoo eventually, but I'd like to see Google improve.