I have been searching the Internet for an answer to this question since I got my iPad a few weeks ago. I think I know the answer based on the info I have found on the internet but I figured I would give it a try here for a more definitive answer (I hope).......
Background: I have a jailbroken iPhone 4 with a Cydia app called TruePrint, that app combined with the Canon app Canon iEPP allows me to print anything from my iPhone to my Canon MP640 printer which is connected to my router via an an Ethernet cable. The Canon app is originally designed to allow printing only photos from your iPhone/iPad (and you can only print from within the Canon app, not from your photo gallery or any other app), but TruePrint basically uses the Canon app as a "driver" so that I can print anything (from any app that allows you to print) wirelessly from my iPhone without my computer being turned on.
There are several apps that allow you to share your printer (both AirPrint capable and not), but the downside is that you need to leave your computer turned on and logged in to a user. But, I want to know if there is a way I can have the same type of printing functionality that I have on my iPhone with TruePrint and Canon iEPP on my iPad 2 (printing to my Ethernet printer with my computer turned off). If I could jailbreak my iPad, this would not be an issue since I would just do the same thing I did on my iPhone. But a jailbreak for the iPad 2 is not available yet.