Can't update 2003 after 2007 install

[Alan]

I had Office 2003 SP3, and installed Office 2007, which automatically erased
MSO 2003. I didn’t want to do that, so I uninstalled 2007 and reinstalled
2003, and then 2007 with custom install to leave Word and Excel 2003.
Whatever caused my problem started with the MSO 2007 install.
Update for 2003 now doesn’t work from Windows update, Office Update, or from
the SP3 file downloaded to my desktop. I get error code 0x8070663. I have
tried KB913754. I have uninstalled and reinstalled everything. I have used
system restore. I do not use registry cleaners. Update 2007 does work. I use
XP Media Center. I have over 200G free space on my hard drive. The notice I
get says that the patch(s) cannot be applied. I have read the other posts and
answers in the group, and I hope that I have answered the usual questions in
advance.
Admittedly, after I get over the learning curve, I will be removing MSO
2003, but I fear that my system is vulnerable for now, and I keep getting nag
screens to perform updates that just won’t work.

 

[Alan]

Additionally, there does not appear to be a reference to MSO 2003 in the
MSOCACHE folder. A missing source appears to be good reason for the problem,
but if the install program doesn't add it automatically, how can it be added?