Hi, I was about to post a different question about this same method. Here's what I use to do case-insensitive search:
var vms = VcPlugin.getAllVirtualMachines(null, "xpath:name[translate(.,'abcdefghijklmnopqrstuvwxyz','ABCDEFGHIJKLMNOPQRSTUVWXYZ')='" + arg_nameToMatch.toUpperCase() + "']");