Can i specify the productversion in a window title?

You can retrieve the version from the AssemblyName.Version property using the following code:

Version version = Assembly.GetExecutingAssembly().GetName().Version;

this.Text = "My Cool Product - Version " + version;

// or with a fancier formatting
this.Text = string.Format("My Cool Product - Version {0}.{1}.{2} Revision {3}", 
    version.Major, version.Minor, version.Build, version.Revision);

Update (after comment):

You can also read the version of the setup from the MSI information stored in the Registry. This is best done based on the UpgradeCode specified by your setup as the UpgradeCode should not change between versions. The following sample program demonstrates how to get the installed version(s)¹ belonging to a specific UpgradeCode:

using System;
using System.Collections.Generic;
using System.Runtime.InteropServices;
using System.Text;

class Program
{
    [DllImport("msi.dll", CharSet = CharSet.Unicode)]
    static extern Int32 MsiGetProductInfo(string product, string property, 
        [Out] StringBuilder valueBuf, ref Int32 len);

    [DllImport("msi.dll", CharSet = CharSet.Auto, SetLastError = true)]
    static extern Int32 MsiEnumRelatedProducts(string strUpgradeCode, 
        int reserved, int iIndex, StringBuilder sbProductCode);

    static void Main(string[] args)
    {
        List<string> installedVersions = 
            GetInstalledVersions("{169C1A82-2A82-490B-8A9A-7AB7E4C7DEFE}");

        foreach (var item in installedVersions)
        {
            Console.WriteLine(item);
        }
    }

    static List<string> GetInstalledVersions(string upgradeCode)
    {
        List<string> result = new List<string>();
        StringBuilder sbProductCode = new StringBuilder(39);
        int iIdx = 0;
        while (
            0 == MsiEnumRelatedProducts(upgradeCode, 0, iIdx++, sbProductCode))
        {
            Int32 len = 512;
            StringBuilder sbVersion = new StringBuilder(len);

            MsiGetProductInfo(sbProductCode.ToString(), 
                "VersionString", sbVersion, ref len);

            result.Add(sbVersion.ToString());
        }
        return result;
    }
}

^{1_{Note that there might be several versions of one product be installed in parallel. In that rare case you would get a list with all installed versions.}}

Here is my solution using DataBinding and Reflection:

In XAML:

<Window ...
        Title="{Binding WindowTitle, RelativeSource={RelativeSource Mode=Self}}"
        >

In code:

public string WindowTitle
{
    get
    {
        Version version = Assembly.GetExecutingAssembly().GetName().Version;
        return "MyTitle v" + version;
    }
}

try this:
System.Reflection.Assembly.GetExecutingAssembly().GetName().Version.ToString();