Yes, you can install different MIKE by DHI 2012 software packages such as MIKE 11, MIKE 21, MIKE SHE, etc, on the same computer.
The MIKE by DHI 2012 software packages can run at the same time on the computer, so if you have an 8 core machine you can run e.g. MIKE 11 on 4 cores at the same time as you run MIKE 21 on the other 4 cores.
Regarding the hardware, please be aware that Server OS is not supported, and it is not recommend sharing the license among different users through terminal services. With a corporate license the software is networked, so I would suggest a reasonably powerful workstation.