What type of Office 2003 did you purchase? Enterprise?
It sounds like it is searching the network for other copies of Office to find an open license or to make sure there aren't other copies of Office installed on the network.
I have a couple of suggestions.
First shut down your computer, disconnect the network cable and reboot. If the respond time is quicker without the network, I would conclude that it has something to with searching the network for something.
But if that doesn't help try this.
I had a problem like this similar in Office 97 on a Windows 98 computer. I finally got it to respond right away by doing a complete disk scan. Once the scan was complete my Office started working correctly.
I think it may have something to do with Microsoft Fast Find. I went through the same mess of updating, changing registry inputs, Defragged like 10 times and then I finally (4 months of trying to fix it other ways) did a Scan Disk (Error Check or whatever its called in the window). When it finally finished...ta da...fast response.
Try it, it might work. Just remember it is going to take a few hours for a thorough scan disk to complete.