Hmm.. i have/had a msi neo4 platinum with nforce4 ultra and ethernet just worked with the 'forcedeth' selection at installation. I didn't need to unplug psu. I am seeing some 2nd hand asus mb's (a8n sli deluxe and a8n-e) which I might buy one of.
if you don't need SLI or additional pci-e for sata/sas controllers - a8n-e is a good choice
as for nforce lan - forcedeth must work with it (if not - unplug powercable )
but a8n-e and a8n-sli have noisy and not perfect chipset cooler, so you may need to replace it.