if there is a single ; to be replaced you could do

$string =~ s/^(.*\(.*);(.*\).*)$/$1,$2/;
[download]

if there's an unspecified number

($a,$b,$c) = split(/[()]/,$string);
$b =~ s/;/,/g;
$string = $a."(".$b.")".$c;
[download]

there's probably a way to do it in single regexp, but I don't have enough caffeine in my blood to see it yet.

/\/\averick