Um, I remember being able to run Arma on the same PC I ran CWA on. The gig and half of ram will certainly benefit you but I think you fall short in the CPU and GPU areas, which are definitely the most crucial areas.
There is a way to reduce some lag by dropping your settings way down and lowering view distance and disabling shadows, anti-aliasing and other things that are not needed to play. The thing about Arma is that unlike CWA, it doesn't set all island objects at the start of the mission/island load. It places different(simpler models further away and then replaces them with more complex models as you approach). It allows for more complex, largely detailed islands but requires a faster cpu and gpu to process the data that is needed to render each model and it's texture.
If you're getting bored of playing it, you should swap up with another game for a few weeks/months. It'll help you appreciate the freedom and potential of BIS titles. I still do not grow bored of CWA. But then, I have Arma and Arma2CO/BAF/PMC to tinker with too. Most of my time is spent jumping back and forth between unfinished projects in each title. I don't think they'll ever get finished, but the point is that I find it fun and challenging to learn as much as I can.