Thank you for the reply!
Long story short - I needed to use special Windows 2003 s/n for vendor installations. Then I was able to register it over the phone! The numbers are here:
http://technet.microsoft.com/en-US/library/dd727762.aspx
Now, long story :smileyhappy::
Yes, I had admin credentials, but this beast didn't let me to login! The only way was to register it over the phone - but I didn't have license number to generate installation ID (the server was installed about 10 years ago!).
Answering another guy's message - to change interfaces in VMware didn't work either. the problem was not in interface type (default one was OK), but these interfaces were recognized by windows as new interfaces and it assigned default network configuration to them (DHCP etc...) :smileysad: I didnt' have DHCP on external network!
So, I installed program on original hardware server to rip the serial number - I got it. used it for installation but phone lady in M$ told me that wrong installation ID was generated (you know this zillion digit-alphabet number which you need to read aver the phone). She said it is a vendor problem - call them. (The original servers were DELL)
I called DELL, they said - Windows is not our problem - call M$!
I started feeling pi$$'d 0ff!
finally after few more phone calls somebody in M$ directed me to the page I gave above. This serial worked fine and provided correct installation ID.