Q:

How to give the option to change the Textbloack foreground-color,size in Windowsphone7

I am completely new in Windowsphone7.i have develop sample application in that i want give the option to change the font-color,Size,style(Italic/Bold) as Dynamically(like RadEditor) .please help me how to resolve this option. 

A:

If you Develop your Application MVVM style then it is not so hard to do this.  You just need a property for every setting you want to set dynamically and then bind to this properties.  And you create a Settings View where you can set the properties  and if you change them you use INotifyPropertyChanged to broadcast that your properties value changed and so every control which is bound to that property will change and redraw. 
GalaSoft MVVM
MVVM Codeplex
Easy MVVM sample Application for Windows Phone 7
The link you found to save an image looks ok, but i did it a bit different, actually from the CameraCaptureTask you already get a WritableBitmap Image and you can save it like this. 
To save the Image:
private void SaveToIsolatedStorage(WriteableBitmap image, string fileName)
{
    using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile. GetUserStoreForApplication())
    {
        if (myIsolatedStorage. FileExists(fileName))
        {
            myIsolatedStorage. DeleteFile(fileName);
        }

        using (var stream = myIsolatedStorage. OpenFile(fileName, FileMode. Create))
                    {
                        Extensions. SaveJpeg(image, stream, image. PixelWidth, image. PixelHeight,0, 100);
                    }
    }
}

To read the Image:
private WritableBitmap ReadFromIsolatedStorage(string fileName)
{
    WriteableBitmap bitmap = new WriteableBitmap(200,200);
    using (IsolatedStorageFile myIsolatedStorage = IsolatedStorageFile. GetUserStoreForApplication())
    {
        if (store. FileExists(fileName))
                    {
                        using (var stream = store. OpenFile(fileName,FileMode. Open))
                        {
                          bitmap. SetSource(stream);

}}                 
    }
    return bitmap;
}

I hope this will work because i wrote it from scratch. :)  
And in your ViewModel you should have a WritableBitmap Property which is bound to your Image Control on your View.  
To use a lot of images and work with them you should read a bit more about this, because somehow SL Images use a lot of memory so you will need to address this problem somehow in the future. 