Well, I’m going to go ahead and say that it is safe. However, there are conditions, the game must be a legit game such as world of warcraft, and the computer must be clean and virus free to start with.
As for vista, I am actually running vista on this laptop, basically because im too lazy to format it. I used to run XP on this laptop, but it is vista now. My laptop is fairly good considering it is a laptop, but while I have vista installed, I cant even play 256 color diablo 2 without lag, but when I had XP on this same laptop, It could run diablo 2 without problem, it could even load sim city 4. Nothing will lag a computer as much as vista. It just spikes the living daylights out of the CPU.
Here is what I would do:
First, consider changing to windows XP or windows 7, and then…
Download a TCP optimizer, watch a couple of tutorials on youtube for the TCP optimizer that you downloaded. Once you know what you are doing, go online and do a internet speed test, and take note of the download speed, the upload speed and the ping.
Once you have done that, open the TCP optimizer and set it to the speed you are supposed to have. save changes and reboot, then do another speed test and see how much faster your internet connection is now. This will usually make your download speed about 500k faster, and will also make upload a good 20k faster, as well as possibly improving ping.
Once your internet is faster, close all programs you are not using, load the game, and see if it runs better. If it is still not fast and smooth enough for you, consider lowering the graphics settings of the game to a lower quality.
IMPORTANT: you must know what you are doing, dont skip the tutorials, there is a risk of ruining your internet connection and a risk of bugs and glitches.