With these two programs you can accomplish most of your
light weight needs for image editinga nd scalable vector graphics:

Irfanview - http://www.irfanview.com/ [1]

Many have used this program to open tiff images and modest editing.  HOWEVER this program can do basic editing like resize, crop, rescale, adjust contrast, adjust intensity and even save to PDF.   

So for a free and quick editor, be sure to google some of the extra features of this application.

Inkscape - http://www.inkscape.org/en/ [2]

Commercial vector graphics programs are expensive $$$.    LIkely you can do most of what you need with this applicaton!