You have links on the "Other versions of : 5.0 , 4.1 , 4.0" section.
Why not go with 5.1 or 5.0 U2 btw?
Anyways, here's the HP custom ISO for 5.0 U1:
https://my.vmware.com/web/vmware/details?downloadGroup=HP-ESXI-5.0.0-U1-15MAR2012_V2&productId=229
And here 5.0 U1 vanilla image:
https://my.vmware.com/web/vmware/details?downloadGroup=ESXI50U1&productId=229