Sorry, Publisher uses a proprietary format that only Publisher itself could open. I'm not aware of any application for an iPad that can open those files. There are some third-party services that purport to be able to convert Publisher files to .doc, but I don't know if those services work well. Otherwise you'll have to copy out the objects and text in the Publisher file and paste them into a Word document which you could then open on the iPad in Pages, Documents To Go, or another app that can edit Word documents.
There are also products and services that say they can convert Publisher files to PDF, if you just need to be able to view them on the iPad.
I recommend you convert the Publisher file into PDF, either with Adobe Acrobat or an alternative converter program. If you don't want to buy one of these converter programs, there are also free online services that do that too. Here's one such service: http://www.pdfonline.com/convert-pdf/.
I had massive amounts of Publisher files which I converted to PDF, transferred to my iPad and saved to Goodreader.[Goodreader has an excellent file management system, including the ability to add annotations to the PDF file.]
I use PrimoPDF, which is free, to do the conversion as it creates a smaller file and also gives you the opportunity to view multi paged PDF's as a book (just tap the edge to turn the page).