I installed pyPdef (http://pybrary.net/pyPdf/) in my Python installation (python27, Windows 7, Eclipse Helios, PyDev 220.127.116.111040403). If I try to use pyPdf, the import line
from pyPdf.pdf import PdfFileWriter, PdfFileReader
is flagged as erroneous (Unresolved Import: PdfFileWriter; Unresolved Import: PdfFileReader), but the program itself is executed without errors!
Can you try updating PyDev to the latest nightly build (http://pydev.org/download.html) and see if it works for you?