Hi Jacek,
We don't have any specific recommendations on how to set up a separate fail over server, however I can tell you that Service Desk wont work if you just copy the files over; you would need to do a proper installation.
It's hard to advise in too much detail because you haven't said specifically what you want to fail over, or how you intend to achieve it - for example, do you only want Web Access to fail over? Do you want the knowledge index to be copied as well? Are you using the NLB/Failover Clustering built into Windows Server? If you are, we have some articles that might give you a few pointers, although they are specific to load balancing rather than failover clustering:
Configuring Microsoft Network Load Balancing (NLB) for Service Desk
Using Service Desk in a load balanced environment
Troubleshooting load balanced Service Desk applications
Hope that helps,
Jon