I have checked at VMware Compatibility Guide: System Search already
They support Dell Poweredge 2950 III , but our model is the first version of motherboard not the third, therefore our hardware is not 100% supported even if I tried to use the customised ISO file from dell.
I have raised the problem to VMWare support engineer in China. They too feel helpless as the software download on their download website is only available to paid customers. They are unable to let me FTP a correct version of the files. I hope they are now communicating the issue with VMWare headquarter overseas so the webmaster can fix the problem on the website.
I think the support engineer also pointed to the documentation that VSA 5.1 is not compatible with VSphere 5.5. So I suspect we are stuck in setting up the systems for testing until VMWare official correct their website materials.