The only VMware product that can auto start VMs without logging in is VMware Server or ESX. ESX would have to erase your hard drive, so that just leaves Server.
Officially, Server does not support "desktop" versions of Windows as hosts. (Just Server versions of Windows are supported.) However most people have success with WinXP as the host, particularly with the older Server version 1. Many people report issues with Server on Vista an Win7 hosts. So just take that into consideration if you ever upgrade your host. That said, Server 1's other limitation is it only supports USB1. If you have need for USB2 devices, then you'll want Server 2.
Me personally, my usual recommendation for autostarting VMs with Workstation or Player is to just put shortcuts to the VM in the Startup folder. Have Windows auto logon. (I prefer TweakUI from Microsoft's Powertoys since it's a simple GUI interface and doesn't require editing the Registry.) Then make shortcuts to the VMs in the Start Menu Startup folder. If you want security, then have a screensaver password. In cases like this, I set the screen saver to 5min. While not as ideal as having the VMs start as a service like Server, I've found very few cases where this workaroun is not sufficient. Autostarting VMs without logging on means your host is really acting as a server, so best to build your host as a server rather than as a desktop.
The fact that Server is problematic on Vista and Win7 hosts and that development of Server seems to have stalled, prevents me from recommending Server on non Windows Server based hosts. But because you have WinXP and that was the one version of Windows that VMWare Server was stable on, you have a very good chance for it to work. I would just recommend you do not upgrade your host to Vista or Win7.
