toma,
You are correct, Proc::ProcessTable does provide a pctcpu option. There are a couple of reasons I suggested parsing top instead of Proc::ProcessTable. The first is because there is no way (that I know of) to change the sampling window as there is with top. The second reason is HPUX does not ship with an ANSI compliant C compiler. This isn't a big obstacle to overcome, but for the sake of portability, I have no issues parsing the output of a built-in command especially one developed by the vendor.

With that said, here is some sample code on how it could be used:
(Much cleaner than my parsing of top)

#!/usr/bin/perl -w
use strict;
use Proc::ProcessTable;
my $t = new Proc::ProcessTable;
foreach my $proc ( @{$t->table} ){
    print $proc->pid , " : " , $proc->pctcpu , "\n";
}
[download]

Cheers - L~R