UPDATE: I observed that after several reboots, the XCPT-HOOK1 (TDSS.e!rootkit) item reappeared every time in McAfee full scans. McAfee Total Protection reported the infection removed each time but the Google redirects persisted and Windows components were still missing (Administrative Tools, cmd.exe, etc.) I attempted many times to download and run TDSSKiller.exe, using different methods, renaming the file, tranferring it to the machine via different means, etc. It would not run, at all.
Finally I downloaded the .zip version, directly from this link: http://support.kaspersky.com/downloads/utils/tdsskiller.zip
, to a clean PC, transferred it to a clean flash drive, extracted the contents to the flash drive, renamed the executable TDSKiller.exe to something random with the .com extension (lksjdf.com e.g.), copied it to the infected machine's desktop and ran it succesfully.
This was the only method that worked for me. It may also have had something to do with the fact that kaspersky.com updates the tool periodically, and I may have finally simply downloaded a version that worked for the permutation I had encountered.