There is a file verification procedure in the Troubleshooting Tips topic, which can identify missing files, as well as potentially corrupt ones.
The DrvMgt.dll file should be in the '..\Divine Divinity\Run' folder. Did you check in Explorer if the file is there or actually missing? If missing it can be re-extracted from the first install disk, from the executable.rar file in the 'disc1' folder (though if you got the div.exe file from that same rar archive, I'm not sure why the DrvMgt.dll file would not have been extracted in the first place).
Osiris.dll should also be in the '..\Divine Divinity\Run' folder, extracted from the root.rar file in the 'disc3' folder on the play CD.
For the memory error, was the error message from Windows or the installer? It could indicate a problem reading the CD, a problem with your memory, or just details about the program crash.
There are a couple memory testing programs you can try. RAM that is starting to go bad could cause random file corruption or read errors in memory intensive applications (game installs, burning DVDs, etc) while not causing any issues with normal operations.
Memtest86 /
MS Windows Memory DiagnosticHave you run virus and spyware scans recently?

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