u can not open jpg files using MS Paint.u have to use softwares such as ACDSee or IrfanView.IrfanView is a free software and supports a LOT of formats.install it and while installing,associate JPEG,JPG files withe IrfanView and then u can open the files.also u can convert BMP(Paint) file to JPG,just use Save As option in IrfanView.
It is available in Digit CDs or download here:-
http://www.irfanview.com/