I was wandering around looking at Hipstamatic photos taken with iPhones on flickr and saw someone ask ... can we do it with Paint Shop Pro?
A lot of elements that create the Lomo effect are easy to reproduce with you break it down and start playing around with layers.
Add the darkened corners of the "Lomo" effect by adding a solid black raster layer (I chose to set to slight transparent). Then use the selection tool with a circle with the feather attribute set to about 100 or even 200 and select a circle in the middle ... then delete most of the dark layer. You don't have to be exact with chosing the center of your image because being a little off-center will add to the retro feel rather than detract.
The end result will be something like ...
If you want a more vintage or retro feel to the colors in your image add another layer with a navy blue color (I used #000040) that has the blend mode set to exclusion.
The end result with a more retro feel to the colors will be...
You can also use "Film and Filters" in the "Photo Effects" menu to add a tint in much the same way Hipstamatic users can add a color gel flash color to images. This is the cooling ... an aqua blue tint.
But the sky is the limit with picking colors and creating a custom filter. The Hipstamatic page shows red, yellow and blue color gel flash bulbs that they reproduced.
If you'd like to add a layer with a grungy effect... see this video tutorial about adding layers that I found on YouTube.