Nevermind then. I asked because I'm not at home right now, and I'm in a code giveaway thing. I think it's kind of stupid that you can't redeem codes online.
As soon as you redeem the code you are prompted to download what the code unlocks. The only way to do that is by doing it on your PS3 or PSP.
You wouldn't be able to use what the code unlocks anyway, so why not just write it down and wait until you get home?
You can redeem the codes on this website. When you log into the playstation website, go under account settings, then click the tab on the right that says manage my account. From there you should see a link to redeem psn/promotional codes.