So you've finally got that iPhone 4 that you've been wanting since launch day, and like so many iPhones out there, it's now broken. Sure, you could go to the Apple Store like the rest of the suckers out there and pay a ton of money for a new screen, or you could be a burly man and fix it yourself (note: opening up the iPhone voids the warranty, so future repairs/issues are all on you) (note 2: if the repair backfires, I'll still think you are awesome). Like most electronic repairs, installing the replacement screen isn't all that complicated, but without a solid repair manual you might as well be trying to fix the Hubble telescope.
Fortunately for you there is an app for that (which you'd have to use on your unbroken iPad) called iFixit. The app comes with thousands of step by step guides for all sorts of things with parts, from cars to Macbook Pro's to your poor iPhone screen. The guides all include high resolution photos, color coated bullets, and an easy to follow, step by step instruction list. Best of all, the app is completely free to use and is funded by the iFixit part store which offers the parts needed for all your repair projects.
Again, fixing most electronic equipment completely voids your warranty and leaves you completely open to dirty looks at your local Genius Bar, but it'll make you feel really really good about yourself. If anything, you could quickly and easily become one of those guys on eBay that buys broken units and fixes them up like new. Discount electronics are awesome electronics, and that is the truth.
Happy fixing y'all! I think I'm going to go find myself a new (broken) computer to fix up with iFixit.