I`m using Leopard 10.5.2 on an AMD64 nforce4 system. It was working perfectly good with Tiger 10.4.10 Tubgirl, but with Leopard I was having troubles with torrent clients like transmission.
The problem is that in the middle of a torrent download the system goes down in a badly way, that is completely stopping the machine.
After some researching in the forums I found a post about a similar problem but on a macbook and a macpro (I suspected it was only a hackintosh related problem). In that thread somebody points out that maybe spotlight is fighting with the torrent client. That is the two are trying to get access to a file that is constantly changing as it´s being downloaded. It sounded logical so I restricted the directories where spotlight indexes files (the downloads directory) in system preferencies-spotlight-privacy.
That was not the cure, but I noted something: sometimes I leave my hackintosh downloading some files via P2P (there is no problem about P2P, just torrents) and when I come back and start surfing the web the system goes suddenly down...just like when downloading torrents.
I suspected a networking problem because I read somewhere about forcedeth network driver (which drives the nforce LAN in the motherboard) being very experimental .SO I shut off the computer, installed a 3com 3c905txnm that I have hanging around and.....IT WORKS WONDERFULLY... and the card is recognized inmediately (no kext editing required).
After doing that, the system was downloading torrents for 48hs till the time Im writing this.
No errors, and no hangs.
I recommend you to buy such a cheap and exceptionally well performer card like the 3c905 series. They have native support in osx.
I hope this post could help someone.

SOrry about my english, I don´t know if it´s really clear.
Greetings from Argentina.

Hola hermano, como te vá?

Yes! Your trick is good, and i think help some guys here.

I'm adding together your 3c905 a Realtek 8139C and D series.

Thanx lasky78, good contribution here.

thank you. This is my first contribution here, but I´m working with hackintoshes from 2006. Maybe there is some more helpful information I could share.
Muchos saludos a todos!

I am having this exact problem. Is buying a new card really the only solution?