There are a few decent choices around. Quick Office and Documents to Go have been around on mobile platforms for many years. Office2 HD is a nice one with connections to Google Drive and Dropbox plus ability to edit the two file types you need.
Apple's own iWork apps, Pages and Numbers can import and export in Word and Excel formats. They're both very nice apps but you may find more formatting and similar compatibility detail type issues with these.
good luck with trying to get the ipad do everything natively. (as if you were on a windows machine), i know i could never get it to
and if you do get it to work right let us know. i'm dying to find out which app will do it.