use strict;
use warnings;
use Getopt::Std;

my %options;
if (scalar @ARGV < 3) {usage()};

sub usage
{
    print STDERR << "EOF";
    \nThis program does...
    usage: $0 [-hcfo]

            -h  : this (help) message
            -c  : config file
            -o  : Fj xcf release file
            -x  : output file

EOF
exit;
}

getopts ("hc:f:o:", \%options);
usage() if $options{h};

if ($options{o})
{
    $source_file = $options{o};
}
else
{
    $source_file = "as.xcf-dist";
}
if ($options{c})
{
    $config_file = $options{c};
}
else
{
    $config_file = 'config.ini';
}
if ($options{x})
{
    $dest_file = $options{x};
}
else
{
    usage();
}
[download]

You can always write that more tidily:

my $source_file = $options{o} || 'as.xcf-dist';
my $config_file = $options{c} || 'config.ini';
my $dest_file   = $options{x} || usage();
[download]

Another possibility is to use Getopt::Long, which IMHO has a nicer API.

Not just IYHO...
Tk::Getopt uses the Getopt::Long API and makes it easy to knock up a simple GUI with loading/saving of options and setting defaults too... You can also override the gui part if you want to take options directly from the commandline

Just a something something...

I have several suggestions.

You should probably change 'f' to 'x' in your usage and in your call to getopts. It looks like you have a bug.

You should probably get rid of the @ARGV check because I doubt it does what you think it does. If you pass these 2 options on your command line, '-c foo -x bar', scalar @ARGV will resolve to 4, not 2, as you might expect. Instead, consider checking the return status of the getopts.

I make it a habit to check if an option is defined, just in case '0' is a legal value:

if (defined $options{o})
[download]

Consider using the Core module Pod::Usage instead of rolling your own usage handler. I second the recommendation to switch to Getopt::Long.