Hi there. I was recently going to buy a new RAM kit for my brother's MacBook Pro, a 2.5GHz Penryn model. Now, when I went in the shop, I asked for PC-5300 DDR2 667MHz RAM. Now, up to this point they didn't know it was for a MacBook Pro. Then I said it was going to be used in one, and they said the RAM wouldn't work in it. Is this true? The RAM I was going to buy was the Transcend model with above specs. I was initially going for Corsair RAM, but they only had one stick left, and, not wanting to take any chances, I changed brands. So can the PC5300 DDR2 667MHz Transcend RAM stick work in a 2.5GHz Penryn MacBook Pro?