client lack when using dfs

i'm runing domain environement .the client folder are redirected to the dfs and the client complain the document open, saving and processing of the document very slow sometimes even hang. i'm using xeon 2ghz and 1 gb or ram server , network is 100mb full duplex. only about 20 user are accessing to dfs every time
client are using windows 2000 and windows xp. why ?when client doing the document ,the document reaction will become very lack sometimes event hang.what can i do???? and how to detect the cause of the problem?????