If you want realistic wet oil painting, with a lot of luster of the wet
oil paint type you can use Deep Paint.
http://www.photo-freeware.net/deep-paint.php
The screenshot there does not show the shiny wet oil colors but they
are available in the program.
It is based on a 3d view of the oil colors, with lighting effects from
a source of light and you can adjust the position of the light.
The wet oil colors are raised up from the canvas, and this gives a 3d
effect of the paint. The wet oil brushes give very shiny colors, which
look very realistic.
I found that the saving to jpg in the program reduced the luster so it
may be better to use copy screen to clipboard to get an optimal result,
so the created painting looks exactly like what you see on screen when
you make the painting.
The wet colors also mix like in real life, when using a brush with wet
paint on other wet paint background.
It can be used in win98 but then you need to save often and avoid
certain operations.