slow download speeds using bittorrent can be caused by many factors.
1. If the seeded file has only a few seeds then it will be slow.
2. If you don't have NAT setup properly and your are not seeding back, your download will be slow
3. your isp may not be throttling but you may experience contention during peak hours as your isp may be oversubscribed.
4 your isp may be throttling.
Here is a link to a wiki that lists legal legit torrent trackers.
http://www.azureuswiki.com/index.php/Legaltorrentsites
most have faq's that you can read.
regarding NAT, setup your router to forward any port of your choosing. take tcp and udp 20000 for example.
so in your router forward tcp and udp port 20000 to your macs ip, eg 192.168.1.x
then in your torrent client specify port 20000 as your network port.
firstly i live in australia. so, how do i check if there are no NAT problems? also with the firewall, how should i have it setup?
once you have setup NAT correctly on your router then use the bittorent client to test the NAT port. Transmission and Vuze/Azureus and others have this functionality.