Things to try:
Sometimes this will help the inital open of a file or table:

* Set the foreground buffer to * approximately 10M.
? SYS(3050,1,10000000)
* Set the background buffer to * approximately 6M.
? SYS(3050,2,6000000)

There are several articles here on the UT about tweaking this value.

Also, you will want to make sure that your MTU's are optimized. This can make a huge difference. Especailly on Win2000 & 2000 pro clients.