u-boot

hello,
im using mini2440 board. im tring to use my own linux and root file system
instead of pre installed one. to do this i need to edit u-boot enviroment
parameters, but auto-boot countdown timer of pre-installed set to "0", so
i cant enter u-boot prompt. wht can i do for this problem.
thnk u

Here is a small quide for installing u-boot on a FriendlyARM board.
http://labs.kernelconcepts.de/_goto/49/Micro24401/#Replacing-the-Bootloader