Providing the books are DRM free (not copy protected) you can load them into either the iBooks app or Stanza. For iBooks just import them into iTunes on the computer, and sync.
For Stanza, connect your iPad to the computer and select it in iTunes. Click on the Apps link at the top of the page. Scroll down the the File Sharing section, select Stanza, then add the books to the file window. No need to sync, the books are added to the iPad immediately.
You can also do this for iBooks if you don't want them in the iTunes library.
You can also mail the books to yourself. When the mail shows up on the iPad, tap on the attchement to download (if surrounded by a dotted line). Whne the attachement is ready, tap and hold on it. An menu should show up with Open In options. You should be able to choose between Stanza, iBooks, or other apps that will read the ePubs.
If you want the books in the iTunes libary and synced with iBooks, don't use the email method. It's been unrealiable when syncing books back to iTunes when books are added by email.
