Internet Explorer 6

I am attempting to use IE 6 with XP on a windows 2000 server based network. The browser will happily open pages for about 10 minutes and then will not open any at all. I have tried to repair & reinstall but still have the same problem. Also as administrator when i change the security setting to low in the Internet Options and appiy it, for some reason it doesn't retain the setting. It returns to Medium. Is there a way to make it stay on Low setting?