File structure

I have a folder on an NT4 server, it contains 953 files in 199 folders and is 199Mb in size, and my Pc’s use Windows 2000 Professional.
When trying to open or attach a file in word or Outlook 2000 I am unable to browse the entire contents of this folder.
The solution so far has been to move files out of the affected folder.
What would cause this problem?