I don't usually blog Windows tips, but since I've been spending a bit of time with Erica's new subnotebook (MSI U230), I've been fighting with Windows more than usual. Apparently, Synaptics is waging a war against physical buttons; pressing both mouse buttons to simulate a middle-click is a pretty standard thing, but there's no obvious way to enable it on one of their touchpads with a recent driver release.
But, it does actually support the behavior, via an undocumented feature (presumably reserved for OEM use). Fire up regedit, navigate to HKEY_LOCAL_MACHINE\Software\Synaptics\SynTP\Defaults, right-click and create a new DWORD value named HasBothButtonFeature, and set the value to 1. Log out and back in again (or reboot), and clicking both touchpad buttons at the same time will result in a middle-click. From there, you can now use Synaptics' software to reassign that action to whatever you'd like.