If your virtual server cannot open OVA files, which by the way are just zips of OVF files, you just need to simply extract the OVF content. There are two ways in which you can do this both detailed below:
Open a command prompt and run tar -xvf nervepoint-1.1-R8-esxi.ova
You can also use a GUI tool like winrar in Windows to do the same
Using vmware ovftool
Download from, http://communities.vmware.com/community/developer/forums/ovf.
Once installed simply run
ovftool -st=OVA -tt=OVF nervepoint-1.1-R8-esxi.ova
The latest VMWare player, Virtualbox and ESXi 4.x can all open OVA files.