accessing db while updating it

[Tao Liang]

I have a table with information about some users.  The data is maintained 
by others.  I have to import it from a text file once a week.  When 
importing, I have to erase all old data and load the table with new values.

The data on valid users should be accessible at all times.  My question is, 
what is the best way to have those data still be accessible while the new 
values are loaded.  I guess I can write lock the table but that would 
probably interrupt the service for too long.

Any help appreciated.

Tao