I'm considering developing a WPF application, to be hosted by a legacy Windows app (C++), and I'm trying to get a better sense of how feasible it'll be to do so, given the broad user base I'm targeting. Knowing WPF targets .NET 3.5, I'm looking for some insight as to what the field looks like right now -- who's already got the runtime, whether it's distributed by Windows Update, if so, how (e.g., as an optional or required download, to which operating systems, etc.), whether XP pre-XP2 supports it (and how), and so on. The current version's got many thousands of users, using all manner of Windows operating systems, and while I'd very much like to leverage WPF to breathe some life into their user experience, I want to make sure I'm not shutting anyone out by doing so, or burdening them with a download they might have to do manually.

I realize most, or all, of this information's out there already, in various places, but I figured I'd ask here first, since I'm sure some of you've probably already gone down this road and have valuable experiences to share. Thanks in advance!