Warning: prerequisite XML::Parser failed to load: Can't locate XML/Par
+ser.pm in @INC (@INC contains: /usr/lib/perl5/5.6.1/i386-linux /usr/l
+ib/perl5/5.6.1 /usr/lib/perl5/site_perl/5.6.1/i386-linux /usr/lib/per
+l5/site_perl/5.6.1 /usr/lib/perl5/site_perl .) at (eval 4) line 3.
   ...
#/usr/bin/perl speedup Twig.pm.slow > Twig.pm
Can't locate XML/Parser.pm in @INC (@INC contains: /usr/lib/perl5/5.6.
+1/i386-linux /usr/lib/perl5/5.6.1 /usr/lib/perl5/site_perl/5.6.1/i386
+-linux /usr/lib/perl5/site_perl/5.6.1 /usr/lib/perl5/site_perl .) at 
+speedup line 5.
BEGIN failed--compilation aborted at speedup line 5.
make: *** [Twig.pm] Error 2
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there's your problem right there. It can't load XML::Parser.

I'm not sure why it can't load it, since it seems to be installed (based on your directory listing) but it appears that you are installing these modules in your own personal directory instead of system wide ... which means that by default, perl scripts you run don't know about it unless you tell them. (in this case, the installer for XML::Twig is trying to run a perl script which is looking for XML::Parser)

Try setting the PERL5LIB environment variable in your shell to know about your personal CPAN lib directory (see the "I am not root, how can I install a module in a personal directory?" qestion of CPANs docs)

The only thing i'm not clear on is why perl Makefile.PL didn't die as soon as it couldn't find XML::Parser ... it's clearly marked as a dependancy, and should have given you a usefull error message.