"The file has reached its maximum download limit. Check that the full text of the document can be meaningfully crawled."
By default, the max download size is 16mb of the file.
You can bypass this by adding a registry entry to HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Office Server\12.0\Search\Global\Gathering Manager\MaxDownloadSize(Dword)
Set MaxDownloadSize to a decimal and max size in MBs. I would max of 100Mb to start.
Restart Osearch Service & start a Full Crawl.
If you add the registry entry, you might also need to increase your search timeout settings in the SSP, as well, to give it more time to crawl the larger files.
"The filtering process could not be initialized. Verify that the file extension is a known type and is correct."
If you can open the file from the link in the search logs, check to make sure that this file does not have an external links included in the file that either are bad or can not be access by SharePoint to be crawled.