Really just get that Asus with GTX 260M and be careful with your online surfing habits.
Download AVG Free Antivirus, Windows Defender and AdWare Anniversary Edition and
do not download untrusted files to your computer.
For example, going to Hulu to watch a streaming television show instead of downloading one from the Internet or Bittorrent. Apply this method to any programming you are interested in. Get it?
With safe computing methods you will be fine. Unfortunately you have to exercise caution no matter the platform you're on.
Mac is no exception.
Example #1
Example #2
My guess is that if you want to play games on your computer you will be disappointed with Mac hardware.
The GTX 260M is roughly equivalent to a desktop 8800GT. The 9400M is roughly equivalent to a 9400GT.
The GTX 260M is much, much, much faster. Do not buy the 9400M to play games on. That's the bottom line.
Also, you will need to run Windows to play modern games regardless of the hardware vendor you buy from. Mac's gaming selection is pitiful.