1006 is our internal error.
Try this: run the setup, wait for the error dialogue, _do not_ press anything. Open another explorer window, navigate to avast temp dir a check if it's full of vpu files.
Because your log says:
08.07.2007 18:43:42 general: Used server: C:\DOCUME~1\user\LOCALS~1\Temp\_av_sfx.tm~a02840
That means the name of the temp dir for avast sfx (it's random)
08.07.2007 18:43:42 file: GetFileWithRetry:DSA_FileVerify(C:\Program Files\Alwil Software\Avast4\Setup\av_pro_core-397.vpu), error: 0x00000000
And this means that av_pro_core-397.vpu was not there or was broken.
Be also sure you've got enough space on the drive and you have write rights to the dir.