What hardware configuration do you recommend to use routeros on it?
I heard that good chipsets are intel945.
Does routeros v3 support multicore cpu?{dualcore, quadcore}
What ethernet cards are best to used, heard that realtec are not ideal, that is better to use intel cards, but intel cards are pretty expensive.
Could you help, also could you post links on that hardware.
What ethernet card is better to use with one ethernet port{more cards in PCI} or more ports e.g 4 on one card.

What hardware configuration do you recommend to use routeros on it?
I heard that good chipsets are intel945.

Anything by Intel is good. go for maiinstream chipsets, the more popular they are, the better supported in routerOS. avoid fancy features like RAID arrays or custom-built motherboards. We found Supermicro's to be good. With Dell we had to tweak around a few settings to get it to work (and then only just, so now we avoid Dell, HP, IBM or other name-brand servers).

Make sure the motherboard has PATA (the old standard, not SATA) support so you can use an IDE flash module instead of a hard disk. I'm not sure if this is possible with SATA, never tried it.

Does routeros v3 support multicore cpu?{dualcore, quadcore}

It supports dual-core, not sure if it makes any use of it though (probably juse uses one core at the moment).

What ethernet cards are best to used, heard that realtec are not ideal, that is better to use intel cards, but intel cards are pretty expensive.

Intel are much better, that is why they're more expensive. Realtek work as well, but you might have some problems if you use VLANs or VRRP. That's the good thing about Supermicro, almost all their server motherboards have 2 Intel gigabit ports built in, which work fine with ROS.

Could you help, also could you post links on that hardware.
What ethernet card is better to use with one ethernet port{more cards in PCI} or more ports e.g 4 on one card.

depends on your needs, budget and available PCI slots. If you only have 1 or 2 PCI slots, I would go for multiport cards so I have room to expand. If I have many PCI slots available, I would go for individual cards as it is easier to replace a faulty one (especially if you're using Realteks or similar low-quality cards)

Hows this. http://www.mikrotikrouter.com for Carrier-Class x86 supported RouterOS solutions.

Intel based systems, are best. Multi-Core is not an issue, we have up to a 8 core systems, that dual quad systems! As well as all front mounted Ethernets, and up to 24 GigE 10/100/1000 Interfaces. Yes I sell these systems. Otherwise, you have a crap shoot on what hardware works. We test, and test some more, and have shipped hundreds of these all over the world.