@trovardo

I too am facing this LAN problem - I have a Via mobo with an AMD 64X2 processor. Unfortunately I have not found any solutions to this problem as yet. Using an external PCI card have marginally improved the situation but I am still getting network drops using the latest drivers/kernels. I have used the following cards:

RTL8139C - Worked with CPUS=1, with Apple Stock Driver, worked intermittently using the PCGen driver using both cores
RTL8139D - Did not work - found no way of getting this to work
D-Link 530 TX - Works using the Rhine driver from pinxue, perfectly with one core, intermittently with both cores

I have also noticed that using two cores has slowed my iphone syncing/itunes generally - therefore there is some dual core issue here too. Insanelymac comments on this being some sort of buffering problem within the kernel - which I think is probably true and changing drivers has had minimal improvement. Additionally playing with PCI settings has had little effect apart from delayed transaction setting - which is having an impact on UDP sessions....

I think this is a core problem with AMD CPUs on particular motherboards - nForce and VIA chipsets being affected... apart from using cpus=1 setting, which wastes a whole core, I have not come up with any proven method to improve the situation... maybe others have?

So in conclusion I am still using the CPUS=1 setting to get a stable system - but need to find a solution - otherwise may have to give up and buy apple hardware...