in reply to
perl depends on perl-base (= 5.8.8-7etch6) ...
This isn't really a Perl question, rather a Knoppix (or, by extension, Debian) problem, so you may get better help at the appropriate forums. Also, installing Debian packages into a Knoppix distribution is not really recommended, it may break all sorts of things in strange and funky ways. So maybe it would be better to reinstall the perl package that came on the Knoppix disk which you used to installed your system (if your current perl is indeed broken). Lastly, really, installing packages by hand is not usually a good idea, configure apt-get correctly and use that, it'll solve all the dependency issues for you.
All that being said, if you really want to go ahead and install this particular package, you should also download the perl-modules and perl-base packages from the same location and install them at the same time (you'll possibly have to use --force-depends for that). This may introduce additional dependency problems as well as previously mentioned funkyness, so don't say I didn't warn you :-)