But truth be told, even now, tone down KDE or GNOME if running close to the line, pare down memory allotment. Granted if you had a real PC you would give no less than a gigabyte of ram to the system to get consistent smoothness, but in a VM, 128MB or 256MB is just fine. Just install VMWare tools. If you are going to run multiple vms, make sure you have a core for a pair of OSs, and plenty of RAM
I have been doing virtualization for years and all it took was some common sense. Back in 2000 I was using Win98 images with 32MB or 64MB of ram. Be smart too, and there are NO issues to deal with.