The issue of having to have multiple build machines can be mitigated several ways. Less expensive is having removable hard drives. 5.25" bays for this sort of thing are availble at places like Fry's and no doubt many online stores. So one removable HD for each configuration.
If you have one very large hard drive, you might partition it such that each partition is a configuration. This is less flexible as it can be difficult to add or change the sizes of existing partitions.
Still another option is to use Microsoft's backup once you have a configuration set up. With the emergency rescue floppy, the backup can be made to completly wipe out your hard drive and restore the backup you select. Have one backup per configuration and your set.
There are other back-up utilities so I am sure there are many ways to accomplish this.
