Well i got further before hitting the ndis.sys freeze.
Instead of grub booting from the unzip'd iso, i grub booted directly from the iso via mem:
map --mem (hd0,0)/ReactOS-LiveCD.iso (hd32) map --hook chainloader (hd32) boot
It starts to load the drivers, but stops after ndis.sys. I dont have a network card, just a hardware modem. Disconnecting usb didnt help.