Check out Derek Seaman's multi-step blog post. It is the most up-to-date guide with tons of information to get you going. It also refer's to many of the installation issues that were found in previous versions of vCenter. As I write this, the blog has already begun making notes for 5.1a instead of 5.1 GA. At this time, 5.1B is out (which I would recommend you install), but you should be able to get through the installation just fine.

http://derek858.blogspot.com/2012/09/vmware-vcenter-51-installation-part-1.html

And as a reference, I would recommend looking over the release notes for 5.1  There is a plethora of info you may want to know as a heads up, prior to the installation.

https://www.vmware.com/support/vsphere5/doc/vsphere-vcenter-server-510b-release-notes.html

https://www.vmware.com/support/vsphere5/doc/vsphere-vcenter-server-510a-release-notes.html

Good luck!