I'm not sure about only having one system restore point.
However, what I do is make a whole system image and store it on an external backup drive. I guess in theory it works the same, by having a working backup, but it's more trouble than sys restore. And it's only really handy if you aren't installing a lot of software.
You can change the size of the space allocated for system restore (System Properties > Advanced System Settings > System Protection), so through that you might be able to manually limit it to one restore point.