What kind of attachment are you trying to send? It's not like e-mail in a traditional sense--the file, first, must be on your iOS device. Then you generally e-mail the file from the picture or whatever, instead of generating an e-mail and then adding the attachment. It's a bit awkward, really, but it works. This is without jailbreaking. Perhaps the jailbroken community has other ways of tackling this annoying problem.
Oh, and another way to get files on your iPad is through iTunes, and loading it onto apps. I like to use the USB Disk program--you can put anything on there.