Not to be "that guy", but make sure you've got the latest _correct_ drivers for your tablet. You should be perfectly fine to make small strokes in photoshop with your setup. If you can make big strokes smoothly, you should be able to make small ones.
I'm using a macbook with 4gb RAM with photoshop CS5 and it works perfectly. My brushes lag sometimes when the spacing is set under 5% so I try to keep it a little over that. The size of the canvas and the number of layers you are using might also have an influence... idk
Mac's are supposedly better for art programs. I have no personal experience though.
Do you have other programs open when you're using photoshop? That sometimes causes lag issues for me. It could also be that your computer just doesn't have the right graphics card or whatever to handle a program as big as photoshop. I'm not a computer person though, so I don't know for sure.