I just wanted to post what worked for me... I know that there are several posts relating to getting the Marvell Yukon 88e80xx cards working on Leopard, but most of them are so long it has become very difficult to find the solution in the thread. To be clear, this solution worked for me with a 88E8038 Ethernet port and a Sigmatel 9250. No need for different kext files or files from previous OSX versions needed. This method has worked with Kalyway 10.5.1 and now with Leo4Allv3 on my laptop, so it's probably a generic fix, at least for the 88E80XX Fast Ethernet cards.

I installed Leo4Allv3 onto my Gateway MT6841 laptop using the 950 video driver that does not have artifacts, but also cannot change resolution. I chose Skge network, Azalia audio, and vanilla kernel. After starting for the first time neither networking or sound worked. I went to

Applications ==> Utilities ==> Terminal

In Terminal I did the standard:
sudo nano /System/Library/Extensions/IONetworkingFamily.kext/Contents/PlugIns/AppleYukon2.kext/Contents/Info.plist

I used the first entry that started with 88E and changed the number to my card's number, 88E8038 in 2 places, and changed the line right after IOPCIPrimaryMatch to also match my card, 0x435211AB. Save with Ctrl-O <enter> and then quit with Ctrl-X.

While still in Terminal, delete the Extension.mkext file by doing this:
sudo rm -r /System/Library/Extensions.mkext <enter>

Reboot, but when the option to add boot flags, use F8 to get to the boot flags line. When it asks for flags, enter:
-x -v

What those flags say are boot in Safe Mode (-x) and show the Verbose output (-v)

After the computer boots up in Safe Mode, reboot again. Now go into System Preferences and select Network. At this point your computer may show an Ethernet connection, or maybe it won't. This may be obvious, but you should have an Ethernet cable connected to the Ethernet port at this time, to verify whether Ethernet is working or not. If you see the connection listed but it doesn't seem to be working, which is what I saw, delete the entry using the (-) key and then add it again using the (+) key. Then click on Apply and your Ethernet connection should show as Connected in a few seconds.

For the soundcard I just used AppleHDAPatcher v1.20 and a text dump for the Sigmatel 9250.

On a semi-related note, after getting my laptop working with 10.5.2, I wanted it to match my desktop 10.5.2 machine. What I did was create an Administrator level user ID on the laptop that I did *not* want to keep -- it was only going to be a temporary user ID. I logged in using that temporary user name, went into Applications ==> Utilities then started Migration Assistant. On the laptop I picked transfer information From Another Mac, and on the desktop computer I did the same thing, but picked transfer information To Another Mac. Instead of using the default of Firewire, I selected Ethernet.

Some applications didn't come over because they need another license, but otherwise everything copied over. One oddity though, is that all folders in my Home directory on the laptop are shades of gray, and even any new folders that I create are gray -- no colors for folders. Maybe a Finder preference that got hosed? I already repaired permissions, but that didn't help, so I'm guessing that it's the prefs file.

how does your Gateway compare to the Gateway ML6720 Notebook? What are your specs?

Because I've tried everything and couldn't get the keyboard working on it (pre- or post-install), and I'm not going to install OS X if I have to lug a USB keyboard everywhere.

My notebook uses the Intel 945GM graphics chipset, Sigmatel 9250 High Definition Audio, 15.4" LCD, Firewire, has 2 gigs of ram and a 160 GB hard drive. It's weird that your keyboard doesn't even work with OS X.

Nuke, dude! I was about to jump when I realised the ethernet failed.
It shows the ethernet connection available but when I plug the cable in it turns on the little leds but they never blink. did it happen to you by any chance? By the way, thank you for the post. I feel I´m very close to get tis working.