All windows computers based on Windows Search 3.0 or 4.0 are not able to index any Mapped Network Drives / UNC Paths. This is a restriction built into Windows Search. Similarly, Google Desktop doesn't search Network Drives or UNC paths.
The reason behind the restriction is twofold:
1) Security - it would be possible for any computer to index any data accessible by said computer. In a poorly secured environment, it could be possible for a rogue laptop to index fileservers with potentially sensitive data.
2) MONEY - if you want those features, pay Microsoft for a Windows Server license, put your data on that server, and then download (for free) Windows Enteprise Search, set up what you want to index, and make those indices available to windows search enabled computers. You have to pony up to Microsoft to get that feature.
This restriction does not apply to USB/FireWire/eSATA/WUSB drives as they aren't fileservers nor are they "shared" by more than one computer at a time. If they shared between computers, they would be NAS devices or fileservers.
N.B. Windows doesn't run on a 323. :-)