Network Slow

The network setup is of win 2003 small business.
Machine with win xp indicate slow network accessing .Tally a account package installed on server and machine with centrallized database. No of times when we try to connect files of tally database it takes more time , if we remove network connection or change insert poing on switch it works fine. Slow accessing of files is due to network congetion or DNS problem.
Please reply my question if any reader have a reasonable solution.