Ram: 667 vs 533

So I'm buying a laptop, good for some gaming, but fairly cheap. I'm getting a barebone Asus, Ati x1600, core 2 duo 1.83.
I wonder about the Ram. Getting a 667 is 40 dollars more expensive (in Canada), and I'm really cutting edges to lower the price to the minimal to play now and upgrade later.
So, two questions:
1) Will it make the difference the upgrade to 667 instead of 533 MHz?
2) If later I got a second Ram, will it work fine if the new one is 667 and the old 533 Mhz? (both working toghether)

Thanks a lot for the help.

 

1) for gaming, go for the faster 667 MHz. There will be a (slight) performance increase.
2) It should work fine. The new 667 will just underclock to the old 533 MHz speed.

 

667 is slightly faster. But if you're saving money, the 533 isn't slow, and should still serve you quite well.

 

1. No, it will not make any tangible difference.
2. Yes, although any 667MHz RAM you install alongside the 533MHz modules will clock down to 533MHz to match the slowest module.