office 2007 install error proplusww.cab

I have 2 new vista Dell laptops. 1 has 32 bit Vista SP2 and the other is a
brand new Dell studio with Vista 64 bit SP?. I purchased office pro 2007 off
of ebay and now trying to install. During install, both machines says that a
proplusww.cab file can not be found. I looked on the install CD and it is
there. I have read many technical threads on this problem and this appears to
be a fairly common install problem but there does not seem to be a definitive
fix. Myself and an IT pro have tried many things suggested by the many
threads. One interesting note, I did notice that the .cab file was very large
255MB. Does this sound right for a .cab file? If it is corrupt, how can I get
MS to send me a new one .cab file. Also, as a final resort, I installed a
trial pro 2007. It works. I was hoping that once installed it would allow me
to use my product key so that I could be fully licensed. The activation
wizard does not let me past the Product ID step as it says the ID I pulled
directly from their trial version is not valid. Any ideas on how to fix?
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Warm regards