To allow the FTP traffic (Data & control), write a accesslist.
for example:
IP access list 101 51 permit tcp any any eq ftp-data
IP access list 101 60 permit tcp any any eq ftp
Also create a Static NAT to access the FTP server
For example:
ip nat inside source static 192.168.1.10 10.16.203.141 extendable
Refer this link to know more about Passive and Active FTP:
http://slacksite.com/other/ftp.html