Hi there,
to connect to different ESXi versions, you need a thick client that is tailored for this ESXi version. They can co-exist together and the binaries are always unpacked to different directories. There is no other way to convince the thick client otherwise.
Download the 5.0 thick client from external source on this handy blog post: VMware: Vsphere Client Direct Download Links - tech :: stuff and then transfer to your required computer via USB stick 
Stop by my blog if you'd like 🙂 I dabble in vSphere troubleshooting, PowerCLI scripting and NetApp storage - and I share my journeys at http://vmxp.wordpress.com/