I use vmware server, it’s brilliant. Here are some reasons to use it.
- Testing slipstreamed Windows disks (service packs and drivers);
- Configuring messy software like msSQL, without it crippling your computer;
- Recovering a backup image ghost/true image to recover some files/settings;
- Running almost any operating system and no dual boot mess;
- Preparing for and testing vpn, ssh, pki, deployment;
- Consolidating servers, have apache2 ubuntu, mssql xp, active directory 2003, all running on the same box. Centralize management and backup policies.