Before I start developing a desktop application, I was wondering how large the installer will turn out to be if I build it in .NET?
Now .NET probably is 5 years old. Do we still have to include the run time with the application? Or can we assume that most user will have it installed on their system? Does Vista ships with .NET pre installed? Lastly can we safely assume most XP users already have CLR installed on their system?
You don't need to include the runtime, the installer detects if it is present at the user's machine and asks to install if not. Nowadays it is safe to assume most XP users have the CLR.
It depends on how you want to distribute the application. If you're putting it on a CD, it makes sense to ship the redistributable along. Otherwise, if you are distributing it over the Web, .NET Client profile is just 25 megabytes. You can configure your setup to download it if it's not available.
.NET was included in Service Pack 2 for XP, in 2004 or so..so I would say it's OK to assume that most people have it by now.
Its easy to determine if the .NET version you're targeting is installed and, if its not, instruct users on where to download it. I'm not a fan of redist-ing the installer bootstrap; its something a hacker would do. Let the user get it directly from the source.
Vista ships with 3.5. XP SP2 ships with 2.0 XP SP2 is required for .NET 2.0, but .NET is never installed by default for XP systems; its always optional. That's pretty much the minimum spec for any MS desktop system; if they are running XP sp1 or earlier I'd avoid them, unless you have specific requirements (embedded systems, dumb/stubborn user base, etc).
edit: I could have sworn SP2 came with .NET 2.0, but I can't find any definitive information about this.