Finally the vSphere Client is supported on Windows 7 & Windows Server 2008 R2:

Windows 7 and Windows 2008 R2 support — This release adds support for 32-bit and 64-bit versions of Windows 7 as well as 64-bit Windows 2008 R2 as guest operating system platforms. In addition, the vSphere Client is now supported and can be installed on a Windows 7 platform.

You can find the downloads and release notes here:

ESX 4.0 Update 1: http://downloads.vmware.com/d/details/esx40u1/ZHcqYmQlcGpiZGVqdA==

Release note: http://downloads.vmware.com/support/vsphere4/doc/vsp_esx40_u1_rel_notes.html

ESXi 4.0 Update 1: http://downloads.vmware.com/d/details/esxi40u1/ZHcqYmQlcGhiZGVqdA==

Release Notes: http://downloads.vmware.com/support/vsphere4/doc/vsp_esxi40_u1_rel_notes.html

vCenter 4.0 Update 1: http://downloads.vmware.com/d/details/vc40u1/ZHcqYmQlcCpiZGVqdA==

Release notes: http://downloads.vmware.com/support/vsphere4/doc/vsp_vc40_u1_rel_notes.html

vSphere PowerCLI 4.0 Update 1: http://downloads.vmware.com/d/details/sdkwin40u1/ZHcqYmQlcHRiZGVqdA

Release notes: http://www.vmware.com/support/developer/windowstoolkit/wintk40u1/windowstoolkit40U1-200911-releasenotes.html