If your accuracy needs are not particularly high, the easiest thing to do is to 
calculate the degrees/kilometer ratio for the local area you are working in and 
just linearly add the required values you want to the coordinates.

Quoting Jan-Oliver Wagner <jan@intevation.de>:

> On Tue, Mar 25, 2003 at 09:48:02AM +0300, Mohammed C. Basheer wrote:
> > This is a beginner's question. Would someone consider to help me to solve
> the problem described below:
> >
> > I have a set of positions of lat/long. I would like to add a few kilometres
> to these positions, and to get the result in lat/long format.
> > Is there any utility softwares (Windows) which I can use to calculate?
> 
> well, you can use the tool proj to project the data into a
> projection where you can easily add discrete distances in kilometers
> and afterwards reproject (I would implement such as a script-solution).
> 
> Depending on your actual data other options should exist as well
> leading up to issueing a full GIS like GRASS.
> 
> You will have a broader range of options if you include GNU/Linux
> into consideration.
> 
> Best
> 
> 	Jan
> 
> --
> Jan-Oliver Wagner               http://intevation.de/~jan/
> 
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