Are they actually crashing and giving you the purple screen? Usually in that case you'll need a memory dump. VMware has a tool for that bundled with vCenter (not installed by default, but it's on the media). Just be aware that with ESXi 5.0, the vmkernel interface used needs to be on a standard vSwitch. 5.1 lets you use a VDS though.
VMware KB: ESXi Network Dump Collector in VMware vSphere 5.x