Please check it at: http://www.imxdev.org/wiki/index.php?title=All_Boards_TFTP
Regards,
Fabio Estevam
Alternatively if you're hosting your files on a windows PC, you can use the tftp server executable included in the SDK tar (L2.6.31_09.12.00_SDK_SOURCE, which you can get from here) and point the Base Directory to the folder where your images are stored.
Please check it at: http://www.imxdev.org/wiki/index.php?title=All_Boards_TFTP
Regards,
Fabio Estevam