OSX problems:
- I can't change screen resolution, it's stuck on 1024x768. Even when i trie dual screen setup, i can only use my 2nd screen (also 1024x768).
- No sound
- No Wifi (havent tried with a LAN cable yet)

Boot problem:
on one partition i'm running Windows7, and i just installed XxX 10.5.6 Leopard on a 2nd partition. When i boot from my windows7 partition, OSX starts. So i can't start my W7 anymore

EDIT: Already fixed the boot problem (with chameleon bootloader).
LAN cable also doesnt give internet connection

We're going to need more details about the hardware in your machine...

...also what distro did you use?

Intel Core2Duo T8100
Ati Mobility Radeon HD3650
Intel Pro/Wireless 3945ABG
Marvel Yukon 88E8040T PCI-E Fast Ethernet Controller

Distro: dont really know, iso is named "XxX 10.5.6 Leopard"