A download accelerator that will work with vBulletin?

First off, apologies if this is in the wrong area, please feel free to yell at me and/or move it. And even more apologies if this has been answered before, I searched and followed the links provided when I input the title (nice feature, btw, may try to steal that for the site I'm coming from ); but I most certainly could have missed something quite glaringly obvious.

Anyways, I'm coming from a modding site which runs off a hacked-beyond-recognition copy of vBulletin, and we're somewhat low on bandwidth and slots, and being donation and ad funded fixing this is an issue. So I'm trying to write an FAQ on setting up a download accelerator which can cope with the getfile.php links. I've already recommended DownThemAll for Firefox users, but am in need of a program which can be used with other browsers.
Preferably the program should be Windows and Mac compatible (Linux isn't an issue as the game we mod doesn't run on it, and Linux users are generally smart enough to work it out on their own anyway), 'though there are Mac-using staff members who can write up instructions on a Mac-only program if no cross-platform ones can be found.
It also must be fully customisable in terms of segments and simultaneous downloads, as downloaders who attempt to establish more than 2 connections are blocked.

Does anyone know of anything to fit the description, freeware/nagware of course? I'd like to point out that this isn't urgent, as we've just finished a donation drive and as such are in the process of buying a new server and a bandwidth upgrade; but I'm sure people will continue to complain anyway once they've filled up the next server's worth of slots

Many thanks
whiterider