Emulating a FTP server as a mapped network drive is not trivial, as the FTP server doesn't supply all the file system operations required by a network drive. Forexample to open a file placed on a FTP server, then the entire file has to be downloaded completely first, as FTP doesn't provide read and write locking capability. This can lead to funny behavior if background services (Anti-Virus, Movie-Preview) wants to scan the files on the network drive.
The following freeware utilities can mount a FTP server as a network drive:
There also exist utilities one can pay for:
Note if using Windows XP or later, then consider mapping a WebDAV folder as network drive
Related Adding FTP server / WebDAV folder as network place