I just thought I'd try to give back to the community that has given so much to me by writing a little tutorial. This technique is one I developed on Macs. Mac OS X has the curl command line tool as part of the default installation. Curl is like a web swiss army knife. You can fetch files, POST data, upload to or download from FTP servers etc... so it brings a lot of functionality to the table which isn't built into FileMaker. I make use of curl through the "do shell script" AppleScript command, which in FileMaker I use through the "Perform AppleScript" script step. Here's a simple 6 line script that lets you take the contents of a container field and upload it to an FTP site. Substitute your container field in the first and fifth lines and your FTP information in the $script variable to make it functional. This script could be extended by actually having variables for the FTP credentials/location too but I've kept it simple here just to demonstrate the technique.
set variable [$file_name; GetAsText(YourTable::YourContainerField)]
set variable [$path_temp; Get(TemporaryPath) & $file_name]
set variable [$path_unix; Middle($path_temp ; Position($path_temp ; "/" ; 1 ; 2) ; Length($path_temp))]
set variable [$script; "do shell script \"curl -T " & $path_unix & " ftp://USERNAME:PASSWORD@FTP_HOST/FTP_DIRECTORY/" & $file_name &"\""]
Export Field Contents [YourTable::YourContainerField; "$path_temp"]
Perform AppleScript [$script]