When both clients are on a single computer, it's not the router.
When they are on a single computer, you may be able to improve things by changing the operating system's thread-scheduling algorithm to background mode.
On Vista, go to Control Panel: System: Advanced System Settings: Advanced: Performance: Settings: Advanced.
Then, under "Processor scheduling," check "background services."
This gives both instances of DAOC equal CPU time, instead of favoring the foreground instance.
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Author of Mojo
www.mojoware.org
www.gaheris.net
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Former PvE server team lead (2005)