Got 2 partitions, each with it's own Windows install: 'work' and 'experiments'. Now, I want to be able to save the 'experiments' partition state and rollback to that state at some point. This would be done while booted on the 'work' partition. The least bloated (e.g. no Acronis) way to do this?
If you're using Windows XP, I would make backups with NTBackup (i.e, the windows backup and restore program)
Otherwise, Macrium Reflect has been a very reliable choice for me.
You might try using a tool like ghost to make an image backup of the partition. Ghost can save these images as a file which you can keep many versions to provide you the rollback resolution you desire. This is a pay for product... If you want something free...Keep reading.
Now I honestly recommend trying to use Clonezilla because it is free and does the same thing as Norton Ghost.
The least bloated way I know is Acronis TrueImage.
Or you could use a virtual machine, e.g. VMWare. You can take a snapshot, do your experiments and then roll back to the snapshot.
If there is a lot of blank space, taking a raw image (using dd), and then gzipping it can be very effective.
dd if=/dev/hdx | gzip > /path/to/image.gz