FTP site working but not accessable with IE

I have a windows 2000 server that I have set up the IIS for FTP everything seems to work with a command prompt but when I try and access it with internet explorer (like and the not techie people will) I can’t get in. I type in the url and a login window pops up, I type the same username and password that works fine in the command prompt and in won’t let me in.
any ideas?