Excellent work Brazlimac, thanks for all the effort! Here goes the "I didn't want to wait for iAtkos anymore"-guide.
You're able to see my set-up in my signature. I didn't get 10.5 working with the BrazilMac DVD, but it was part of my personal success.
1. I've got 2 harddisks, number 1 is set-up with Uphuck's great 10.4.9 r1.3i, I use that one to go for Leopard on my second harddisk.
2. Fire up disk-utility and set-up 1 partition on the Leopard harddisk, so you get GUID capabilities (remember to click on the harddisk itself and not on a partition in it, otherwise the partitioning commands do not show up).
3. After creating the partition called Leopard, I erased it as a Mac Journaled scheme just to be sure of a clean system.

4. I used Kalyway's method of preparing the partition for booting. I must mention that before I used this, I also tried to make it bootable by manual commands as shown in BrazilMac's method. Not sure if those actions remained after my erasing the harddisk..
5. On with the EFI 8.0 pack, modifying and running the EFI.sh as root. Making sure that no errors show up during the installation.
6. Rebooting and installing Leopard by use of the ToH DVD package (this kernel actually works, while Brazilmac's didn't on my set-up).
7. Rebooting and starting-up Tiger again, this time using BrazilMac's PostPatch process. I did it manually however, because I didn't want my ToH kernel to be replaced ofcourse. I also had some problems with the script not being able to find some kexts or something, so doing it manually assured me of a good process.
8. Don't forget to set the right permissions to the Extensions (755) and to the ToH kernel (644) and making them root:wheel.
9. Reboot, make the second harddisk the Master (Bios) and press F8 during startup. Use -v to boot verbose mode into Leopard. This worked for me the first time, not doing verbose crashed it for some reason.
10. Install the NatitX1600.r1v3 drivers for Ati cards. This script also gave me an error, I suspected it to be a failure to the ability of the script giving the kexts the right permissions. Just give the entire extensions directory the 755 permission again and chown it root:wheel.
11. Rebooting now, gave me crashes (code 0x00000002 or something similar). So, found on this great forum to use -legacy after pressing F8. That worked again and everything from my card to the monitor is recognised, full QE etc. Strangely, I didn't have to use the -legacy after that. But if needed, you can always put it into the boot.plist file.
Now to get networking working, I transfered all my setting and apps from 10.4 to 10.5 during the install process. And my USBWirelessUtility is starting up, recognizing my WUSB54GC Linksys stick and connecting, but I can't get onto the Internet. Only Firewire is set on my network settings and the network assistance utility crashes. Any ideas anyone?
Thanks for all the usefull guides on here!
Cheerz, Vincent