If you want to have the possibility to restore data on a database while it is already online (i.e. whenever its primary filegroup is online) you can do so only if you are running the Enterprise Edition (or a Developer Edition or an Evaluation Edition, both of which behave exactly like the Enterprise does. The only difference among them three is their licensing.)
Using this feature and with a correct design of the physical mapping between tables/indexes and the files where those structures will be allocated, you can minimize the risk to have a complete database outage and in the event the big disaster would still hit you, you could dramatically reduce the time it would take you to bring the service online and partially operative while the remaining less critical data continues to be restored.
This post is part of the a series I decided to call “Understanding the value of the Enterprise Edition, one feature at a time” which I started in September 2011 and will grow on a weekly basis, having a new post incorporated to the family every Friday.