I can write Arabic/Urdu/Persian on MS Word or Notepad just fine, but whenever I insert any English word or number, the sequence is just disturbed and seems like the all the
In word processing, you have a main text direction which is either left-to-right or right-to-left (or top to bottom, but let's ignore that :-), and you have a text direction for individual characters, which will also be left to right or right to left.
The word processor splits the text into chunks of strings with the same character ordering, then displays these chunks according to the main text ordering.
It seems that your main text ordering was left to right. As long as all your text is arabic, there is just one chunk with arabic text. You see already it is displayed left aligned and not right aligned because the text ordering is left to right. The characters are displayed right to left because that is how arabic is displayed.
When you inserted latin text, you had three chunks: Arabic, latin, arabic. These three chunks are displayed left to right because that is the main text ordering. That would be fine for text that is mostly latin (like "The arabic words for dog and cow are ... and ..."). For text that is mostly arabic with the occasional latin word, you need to change the main text ordering to "right to left".
You need to add an invisible RLE Unicode Character at the start of the line [^]. It's : 0x202B hex = 8235 decimal or RIGHT-TO-LEFT EMBEDDING (RLE). It's necessary for Notepad but MS-Word is able to handle it. you need to right align your text correctly.
How to enter RLE: http://www.fileformat.info/tip/microsoft/enter_unicode.htm