The CTAN page contains a link to oberdiek.pdf which lists ifpdf. The webpage itself doesn't seem to (at least not from my case-insensitive search). I also couldn't find it from searching the source code for the page (AFTERNOTE: This is because it shows up as if-pdf in Microsoft Internet Exporer!). I would have found it if I looked in oberdiek.pdf, but I probably would have been confused by the disparity between the webpage summary and the document. So thanks for clearing that up, as well as for pointers on how to check for its presence. In particular, from web searching, the findtexmf command seems to be specific to MiKTeX and one needs to know th file to look for. This can be found in the ifpdf documentation under Section 4.3 (Package Installation).
I was hesitant to actually rely on loading the package as a test because I'm not too sure what kind of measures LaTeX resorts to in order to avoid crashing when it doesn't find a package. I suppose "nothing" is the right answer.
The thread at http://latex-community.org/forum/viewtopic.php?f=9&t=24134 also suggests "texdoc oberdiek". I issued this at the DOS command line, which made it abundantly clear that ifpdf is present.
AFTERNOTE: Because of the browser wrinkle in searching for package names, described above, one really needs to delve into the PDF documentation. Unless you are guaranteed to be alway using a browser that is immune the problem described.