What you need is the Euler method in combination with vectors. There's a good tutorial (including header) around here, that does exactly that.

You'd apply a vector Force on a mass, which because of F = ma results in a vector Acceleration. Then with Acceleration, a new position can be calculated using the Euler method:

v += ( F / m ) * dt;
pos += v * dt;

Note that F/m is the acceleration and dt is the change of time at which you want to apply the new calculation (which could be the time between frames). The vectors are [v, pos and F], [m and dt] are scalar numbers.

Here's the tutorial combining the Euler method and Vectors:

http://nehe.gamedev.net/data/lessons/lesson.asp?lesson=39

Ofcourse, note that the Euler method isn't the most accurate method of position calculation around, but it's simple, easy to understand and it works. Try it first before trying others, such as the (Time Corrected) Verlet Method. But I doubt you need anything more advanced than the Euler method.

Good luck,
Stemic

Well, I hate to always cite the same references, but they're really the best ones I can think of for 2D physics. So here goes:

1. Chris Hecker's articles (I should find the url so I can just link to it...) Great overall, but especially useful in that it covers everything in 2D before moving to 3D.

2. 'Physics for Game Developers', by David Bourg. Some people don't like this book, but FWIW it does cover rigid body dynamics in 2D, along with code samples.

For 3D, I again recommend Hecker's articles, along with David Baraff's papers and Dave Eberly's 'Game Physics'.

'Hope that helps.