Now that everyone has told you why it doesn't work, here's one solution to getting it to work:

 if ($_ =~/^(\w+);(\d+);$/ && $_ !~/^\#/) {
  print "DEBUG: use constant $1 => $2;\n";
  eval "use constant $1 => $2";
  #...
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The idea is to use $1 as a bareword, and $2 similarly. Note that this doesn't work so hot if $2 could be a string (which it isn't in your case). Unfortunately, it makes all your constants not easily accessable: you'll need to call them like MEMINUSEWAR() (with the parens) or similar. Barewords won't work.

Another alternative is something like this:

use strict;
require constant;

while (<DATA>)
{
    if (/^(\w+);(\d+);$/)
    {
        #eval "use constant $1 => $2";
        constant->import({$1 => $2});
    }
}

print MEMINUSEWAR();

__DATA__
MEMINUSEWAR;2000000;
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Don't do that either. The best idea is to take all these values and put them in a hash - even a global hash. And access them through that.