Simple, free and gets the job done
Great virtualization program, free and very complete.
Can emulate every OS, including USB and shared network directory.
Excellent PC virtualisation software. Open source edition available under GPL license, also a commercial version available same as open source version but with RDP support to connect to remote virtual machines (including USB connectivity). This version is also free for personal and educational use, personal use includes personal commercial use, with just one person (yourself) using it at a time, if you will have multiple users connecting to virtual machines, either use the open source edition or if you want the commercial version, contact the owners to purchase a license. VirtualBox was owned by Innotek, February 2008 it was bought by Sun Microsystems, who are also supportive of open source software (check out open office). VirtualBox has support for many guest and host operating systems, including many versions of Windows, Linux, Mac etc and Suns own Solaris OS. Support includes some Windows and Linux 64bit versions and PAE support (in guest OS, needed for Ubuntu Server). All you need is spare hard disk space for each VM you create and spare memory for the currently running VM's. 2GB RAM and 100GB HDD will give you loads of possible configurations. Even just 256MB RAM and 10GB HDD is enough for Windows98 (with 64MB virtual RAM, 1GB virtual HDD) running as a guest VM on a Windows XP host, you could probably run a few very small (forget big ones like Ubuntu) Linux OS's too. The virtual machines are well contained, great for web browsing or trying out new software without risking your guest OS. Brilliant, give it a try.