How can I find a full short story, The Furnished House by O.Henry, online through COM Library so I can cite it as my primary source?
The Library does have a print copy of The Complete Works of O. Henry by William Porter which does include The Furnished House, the call number to this 2 volume book is (PS 2649 P5 1953)
You are looking for an electronic version. Using Libguides, select the tab, American Lit LibGuide, Find Full Text Poems & Short Stories (link below).
Google Books is another source you can search, here is a direct link to The Furnished House by O. Henry : http://books.google.com/books?id=Fys-AAAAYAAJ&dq=o%20henry%20the%20furnished%20room&pg=PA239#v=onepage&q&f=false
You can also download the e-book to your mobile device. Instructions on how to download are in the Google books LibGuide (link below) on the Free Google eBooks page in the Download the Classics box.