ONTAP 8 is a 64-bit OS that requires CPU virtualization flags to be enabled. You need to enable VT support in your BIOS. Just clicking Yes doesn't help!
Restart the machine you are running VMware Workstation on, enter BIOS (Del, or F1... but might be some other key) and search for CPU options. You're looking VT-x or something along those lines. Then enabled it -- it is usually disabled by default. Save, reboot and then try again.
The ONTAP 7.3.x simulator does not need VT-x. The 7.x simulator runs inside Linux. I mainly use that, since it only requires a small amount of RAM (meaning you can run more simulators). You can use Ubuntu Server, give it 128 MB RAM for itself and (minimum) 110 MB per simulator. That way, on 1 GB RAM, you can run 8 simulators (or 2 cluster pairs - ie, 4 filers). I have several Ubuntu Server VMs on Hyper-V running numerous 7.3.x simulators, very useful for simulating almost anything.