This thread was started in 2006. You should have started a new thread. Event though your question is similar, a new thread will get more responses.
You can download the specs for your instrument at NI's website. Just go to ni.com and type in your instrument (PCI-6602) inside the search box. From there you can find the spec sheet. If the device doesn't support hardware timing, you will have to either find a device that does, or change the timing scheme.