Perl:
my $vote = $query->param('vote');
my ($voteyes, $voteno);

if ($vote == 1) { 
   $voteyes == 1; 
} elsif ($vote == 2) {
   $voteno == 1;
}

$template = param(voteyes => $voteyes,
                                 voteno => $voteno); 

HTML:
Yes: <input type="radio" name="vote" value="1"<tmpl_if voteyes> checked</tmpl_if> />
No: <input type="radio" name="vote" value="2"<tmpl_if voteno> checked</tmpl_if> />