Cannot install TWAIN driver - run preflight failed

Question

I am a Windoze refugee who is helping my father clean up his messy iMac.
He has a Brother DCP-165C printer which he cannot use to scan.
Mac OS X 10.5.8 is up to date, I have recently run the verify disk utility and fix file permissions (as part of my efforts to fix this problem).
I have seen and followed a number of posts in  my attemps to fix it and can summarise my efforts as follows:
De-installed all Brother drivers as per their instructions for OS X 10.5.8 on their supprt website.
The Brother printer driver package installs fine so in repeated attempts I have used various postings to de-install them, they all follow the same theme, but this one appeared a bit more comprehensive https://discussions.apple.com/thread/1881546?start=0&tstart=0
I have created a new user (with admin privs) and tried using that to install since I read that files in the users home can interfere with an installation - no joy.
So I finally took the plunge and extracted the preflight script out of the package and ran it in terminal. It's a perl script which gives the following error:
Can't locate Foundation.pm in @INC (@INC contains: /Library/Perl/Updates/5.8.8 /System/Library/Perl/5.8.8/darwin-thread-multi-2level /System/Library/Perl/5.8.8 /Library/Perl/5.8.8/darwin-thread-multi-2level /Library/Perl/5.8.8 /Library/Perl /Network/Library/Perl/5.8.8/darwin-thread-multi-2level /Network/Library/Perl/5.8.8 /Network/Library/Perl .) at preflight line 12.
BEGIN failed--compilation aborted at preflight line 12.
Now that sounds pretty terminal, but, the secret I haven't let you in on is that I installed the TWAIN package fine last week. I don't know why (or am even certain if) it stopped working, but we had some problems with the printer.
So my conclusion is that I should be able to get this missing perl component, but perl is something I know nothing about.
thanks in anticipation

Answer 1

Solved!!!
Once again thank you BDAqua for keeping me pointed in the right direction.
After some serious research:
@INC array is set when perl is compiled, it is actually built into the perl binary when you run Configure before compiling..
So it cannot be changed without re-compilation. Likewise, it cannot be broken without re-compiling
/System/Library/Perl/Extras/5.8.8 is not actually in the @INC array, Apple use none of the accepted methods (or so I believe) of adding it, they have a file in /Library/perl/5.8.8 named AppendToPath which contains:
               /System/Library/Perl/Extras/5.8.8
                /Library/Perl/5.8.6
                /Library/Perl/5.8.1
The references to previous versions are there for backward compatibility.
It is also poosible to create a PrependToPath file. As you would expect PrependToPath adds directory(s) to the beginning of the search, and AppendToPath to the end.
You can list the contents of @INC with this command:
perl -e 'print join "\n",@INC'
All I did was run Pacifist to verify the directory /Library/perl/5.8.8 and it reported only 5 files found out of 50, so I just asked it to install the directory structure. That was it, fixed, the TWAIN drivers installed.
For background read:
http://www.perlmonks.org/?node_id=486084
http://www.perlmonks.org/?node_id=385469
A must-read is
https://developer.apple.com/library/mac/#documentation/Darwin/Reference/ManPages /man1/perlmacosx.1.html
which details how perl s configured on OS X.
which contains this important and amusing snippet:
"If all else fails and you want to really, REALLY, start from scratch and remove even your Apple Perl installation (which has become corrupted somehow), the following instructions should do it. Please think twice before following these instructions: they are much like
conducting brain surgery to yourself.  Without anesthesia.  We will not come to fix your system if you do this."