Few things:
First off, it is still alpha and as such they have LOT of stuff running in the background. Those debuggers etc are taken out prior to release, but will be there up til release. I've been in many Alpha's and Beta's, and everyone has been laggy. Come release, no issues that were really engine related.
Next, optimization is the last thing that is done for the game. So if you want 60+ fps and buttery smooth, non-crashing game play, just wait til release.
That being said, many have given great feedback:
Step 1: Get an SSD. Ideally 500GB+ would be best because as the SSD fills up, the SSD slows down. When you do get an SSD try and keep it only 75-80% full.
Step 2: Since you have the 3GB, try and grab a new video card. RSI's own website has stated minimum GPU is one with 4GB of VRAM. Yes, I know its hard to grab one at a reasonable price, but auto-notify is your friend. There are some deals out there if you are patient and look. Also, keep any eye out on forums any maybe think about getting used.
Step 3: Look at setting up a 16GB page file. Have heard a few testies saying how well it works with SC.