I got the same problem with a Dell Poweredge R410. I have ESXi 5.0 installed on it (exactly the same config, just on a different set of SSD's) without any problems. I tried to install the 5.0 U1 and the 5.1 U1 versions of ESXi and both show the same problem. The installation simply stalls at a certain percentage. Last night I let it sit there all night without any progress.
Did you get anywhere Janine?
-Felix