Logging onto NT FTP site from a mac

I have an FTP site on an NT platform, which we use to exchange large files with third parties.

We are having problems with MAC users being unable to log into the site to upload files, the latest being a user who is using Netscape as his browser.

Short of teaching them to use FTP, is there an easy way for MAC users to authenticate to our FTP site so they can upload files. I really don’t want to enable anonymous access.
Many thanks

Japes