See that sticky up there? The one that says "Flashing How To"? Read it. There is a link in the first post for what you are looking for.
Thus the reason for a sticky, so people don't clutter the forum with these type of posts. Come on, man, it's not that hard to search, or even just take a glance at what is stickied.
Edit: Since you'll probably miss it, the link is a rapidshare link to RUU.zip (ROM Update Utility)
Edit again: Here's the link to the Sticky if you can't find it on your own.
http://forum.ppcgeeks.com/showthread.php?t=17473