I bought my 17" 1.33 PB with a 1 gig chip in it - so 1 slot is free. Just upgraded to OS 10.3.4 I recently purchased and installed a 512 chip from crucial.com (I had been told by experts that their ram was top notch) ($100). It doesn't matter if it is in slot 2 (with the original 1 gig chip in slot 1), or alone in slot 1 - my mac now freezes very quickly. (Needless to say - my PB runs fine when the original apple 1 gig chip is in it alone) I'm going to swap the new 512 out with a replacement from Crucial (they were very responsive) but what a guy from the Santa Monica Apple store told me today was cause for concern..... He told me that he owned an identical 17" Powerbook.... and he had gone thru exactly the same aggravation. He said he went thru many exchanges with third party vendor ram... and finally had to use 'apple' ram. He explained that apples are very, very picky about ram - and ultimately apple ram is the way to go. (no he doesn't get commission) here is the drag - a 512 chip from apple is $300 - a 1 gig chip is $700 Is this crazy? What on earth is up with this?