You shouldn't have a problem selecting, formatting and installing Win7 into the one partition. The installer should not touch the other partitions. However the Win7 install program will probably make the Win7 partition the active partition that is booted. If the install program does not recognize the other two server partitions as bootable, then you will have to use an editor such as EasyBCD (after the installation) to install those alternate boot options.
Note: Windows 7 is installed on C drive.
Actually this is not going to help you identify which partition to use during the install. Windows always assigns the C: drive letter to the partition from which it has booted. For example, I have a dual-boot PC that has WindowsXP and Windows7, each installed in their own partition. Each OS reports that its partition is the the C: drive.
You should run the Disk Management Tool, which is one of the Computer Management Tools under Administrative Tools. You need to learn how to identify your existing Win7 partition by its size, partition number and relative location, not by its drive letter. Unintentional clobbering of a partition during an OS installation is typically (or always?) due to selection of the wrong partition for installation or formatting, rather than the install program writing beyond the selected partition.
BTW during the installation, when it's time to select the partition for Win7, you will have to first click the Drive options (Advanced) to expose the Format button.