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OK, before anything else, have you gone to portforward.com, and run an external port scan to see if port 21 is in fact open ?
Yea some vendors like comcast home have 21 blocked.
While I could go through setting up IIS I'd recommend you download filezilla's ftp server. It's setup is pretty easy.
Pretty much you do the following:
Setup your machine with a static ip address on your network outside of the dhcp pool.
Forward the ports you want to use. Pretty much with something like filezilla you will have the main port(worth changing as some home isps block 21) and some extra passive ports. Pretty much extra ports to help traffic through. You need to do this on your firewall. You might need to do this on any software firewall you have as well although you should just be able to allow filezilla through the windows one.
Know your external IP. You have services like no-ip which has free versions. You can also hit www.whatitmyip.com and just get your external address.