Helloo
Is it better to buy the mikrotik router itself or setup the mikrotik software on a normal computer with 2 lan cards , and what is the difference between both ?
thanx
With Routerboard ™ hardware you will not have to worry about “will it work with my hardware?”
With a “PC” you CAN get more speed.
There is one “Industrial” rack mount out there built for RouterOS, it is a 3rd party, but I have been told it is a good option..
“Home brew” can be faster and less expensive IE $$$/pacets per second. but you need to keep in mind that you MUST follow the supported hardware list…
Remember… If it is not in the hardware list, there is NO driver and IT WILL NOT WORK !!
Craig
csickles is right.
The major reason for failures with PCs are “old hardware”! 
Industrial is the way to go!