Hello Kltaylor,
You can run the VI-client on a Vista X64 but you have to modify the .msi package with orca msi editor.
see this dutch website for some screenshots and weblinks for this problem :
see below my summery
- start the install of th VI-client and don't click on OK when the warning message appears
- search for the extracted VMware Infrastructure CLient 2.5.msi
- open this file with orca msi editor
- open table InstallExecuteSequence and look for the line LaunchConditions. remove this line
- open table InstallUISequence and look for the line LaunchConditions. remove this line also.
- save the newVMware Infrastructure CLient 2.5.msi file
- install the VI-client on Vista x64 : msiexec /i "VMware Infrastructure CLient 2.5.msi"