I downloaded and tried all the softwares. I did not find Gimp any easy to learn, so I abandoned it for now. Vicman's photoeditor and smoothdraw both do not allow me to make basic shapes like circles, squares etc, hence they are of no use to me. I am currently using all these softwares (Microsoft Paint, Photofiltre, Inkscape and paint.net) to produce the picture that I have attached here . Since I am familiar with ms paint, i found paint.net very easy to work with. Look at the picture and give me your comments. Please note that different images were created in different software and finally assembeled in ms paint.
*www.geocities.com/microrao/img/T_cell_response.gif