For certain reasons I have chosen to dual boot XP and Vista and not to hide
the Vista drive so as to prevent XP from removing Vista's system restore
points. Until recently I would manually create a restore point each time I
returned from XP to Vista. Lately I have been using a script that creates a
daily restore point on starting Vista as discussed in this article. While
the article was written for XP, I find it works equally well in Vista.
http://windowsxp.mvps.org/checkpoints.htm
Even if you aren't interested in using the technique, the article has an
good description of when automatic restore checkpoints are created.