Corel does not offer an automatic vignetting function on X2. To do it manually I use the Lighten/Darken tool with the hardness set to about 30, the density to 100, the step to 1, and opacity set to 30. Darken the corners (and sides if needed) to achieve the vignette look you want. Be sure to right click to darken (left click lightens the image). Vary the hardness and the opacity to control the effect. I hope this helps.

By the way, I now use PaintShop Photo Pro X3 and it works the same way to vignette. X3 is great.