VMWare has a bunch of lovely options for you! Virtualize is the key word! Crawling (slow) virtual machines are a thing of past (ya, it used to be painfully slow before, make this technology kind of useless, especially on low-end hardware). The latest breed are "almost" comparable to real hardware performance. If you want to try your hands on virtualization, check out one of the following free (yes, totally free) options from VMWare:
1) VMWare Player:
Just play your VM like you play a movie. Great if you want to try a new OS or bring up an OS for casual use! Just load your VM, start it and you are ready to roll! Needs a host OS like Windows to run this. Perfect for desktop/laptop users.
2) VMWare Server:
A little more advanced than VMWare Player, more features, more customization. Remote management of VMs possible. Use this if you want to host it on a server and then access it remotely. Needs a host OS like Windows or Linux.
3) VMWare ESXi Server:
If you want more performance and has better hardware, then you should go for this instead of the above. This is a bare-metal hypervisor (means, doesn't need any host OS, therefore direct access to hardware and way too faster and lighter). Install this directly onto your server (as your base OS) and it gives you everything you need for a software enthusiastic, developer, tester or even a small business! It is a carrot from VMWare to get you to try this (and fall in love with and get addicted to it), with an upgrade path to their other licensed advanced products.
Only catch is some missing advanced features and a cap on physical and virtual hardware.
Comparisons between ESXi (Free) vs licensed products (ESX etc)
VMware ESX and ESXi 4.0 Comparison (latest version)
VMware ESX and ESXi 3.5 Comparison
ESX vs ESXi
VMWARE VSPHERE 4 ESSENTIALS BUNDLE LICENSE
VMWARE VSPHERE STANDARD LICENSE