I’ve been using virtualbox (http://www.virtualbox.org) instead of vmware gsx / vmware server (http://www.vmware.com) because the lack of support for vista as the host operating system. Several things are very, very nice: the ability to share directories on the host with the virtual machines (also cross platform), and cut and paste support from host to VM and back. But the main reason is VM’s which (apparently) use more than 1024 MB of memory take ages to startup using vmware, and the entire host is blocked.
The networking of virtualbox a weak spot, that’s something which is better in vmware. A default virtualbox VM is not reachable using the network. It is possible to make the VM reachable by SSH:
vboxmanage setextradata test "VBoxInternal/Devices/pcnet/0/LUN#0/Config/SSH/HostPort" 2224
vboxmanage setextradata test "VBoxInternal/Devices/pcnet/0/LUN#0/Config/SSH/GuestPort" 22
vboxmanage setextradata test "VBoxInternal/Devices/pcnet/0/LUN#0/Config/SSH/Protocol" TCP
“test” is the name of the VM, 22 is the SSH port of the VM “test”, and 2224 is the port which can be used on the host to reach the VM. Protocol to use is TCP.