Yes - any flavor of ESX 4, ESXi 4, ESX 4.1 ESXi 4.1 all requre a 64 bit processor to install or run. ESX 3.5 and ESXi 3.5 do not have that restriction and MAY run under your VMware server - there are a few things you have to do to make that work. If that is something you want to pursue let me know and I will find the checklist.
If you are set on ESX(i) 4.x you will need to get a new laptop that supports 64-bit in order to run it under VMware Workstation - that is a doable thing with the right hardware. If you are looking to do that be sure to shop for a model of processor that supports either the Intel VT or AMD AMD-V virtualization extensions. It will run without them, but it will also be unbearably slow.
Good Luck
