Free software for mounting an FTP share as a writeable folder in Finder
You could create a tiny Automator application to do the job.

Inside of Automator, add the following two actions to your workflow


"Get specified servers"
Specify your server/servers in this action as follows: ftp://username:password@yourserver.com
"Connect to servers"


(The names of the steps might not be a little off since I'm not running an English version of OS X)

Save this as an application and start it whenever you need. You can also make it a startup item in System Preferences > Account under the Startup items tab.