Hello Samuel,
Networks will take twice to three times as long for the same search as a local search, assuming they are fairly new. It'sprobably not an issue with the server, but the network hubs and routers. Replace them with Gigabit switched hubs to get something to transfer the data up the wire.
Also, consider GridView and GridView Server if this is a common requirement (although I will admit that this solution is probably about the same price as buying a new server). Perhaps they might also consider renumbering their customer codes so that they can use the Finder to "guess" at a customer code from the name.
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Andrew Bates