Don't want to necro this, but I had to basically mount the VMDK to a different system to grab the vxlan.zip file off of it. Could not download it using IE or Firefox. My suggestion is to open a ticket with VMware support regarding the inability to download from there. Additionally, there are repo xmls in there that you can't refer to in powercli as well.
In fact, you can't download anything. Plus the docs don't seem to reflect 5.1.2a build numbers in the filenames they refer to.
Multiple problems here.