MS07-017 is a re-release of an earlier patch against a vulnerability in Animated Cursors. Apparently when the code was created for the first fix, the rest of the code wasn’t audited and another vulnerability was recently found. The patch can be found on Microsoft’s website over here
This vulnerability affects all versions of Windows from 2000 through Vista, so you’ll definitely want to patch this one. Also, there’s at least 4-5 public exploits available for this one. You can be certain that it’s being exploited in the wild.