XPS M1330 w/ 8GB RAM -- Is this available only on 64-bit Vista OS?

Firstly you don't want to buy any accessories / RAM from DELL as they are too expensive. Even when buying a new laptop, always spec it with a lower RAM and Hard disk specification as most of the time it is cheaper to buy the parts like these externally and upgrade them yourself. Head over to www.crucial.com/uk

In respect of the 8gb RAM, assuming you have a motherboard/bios that supports it (I am sure if the earlier 1330's supported more than 4gb of RAM (2x2gb), although this could have been because 4gb sticks were not available then) then you can pop this in regardless of your operating system. The problem is that if you are running a 32bit operating system such as Vista 32, then the operating system will only use about 3.2gb of that RAM. The reason for this is that 32bit operating systems can only address up to 4gb of memory but you have to remember that other devices such as your graphics card has memory that the OS needs to address and as such when you take this out of the equation, it leaves you with approx 3.2gb that the system directs to your sticks. 64bit OS does not have this limitation and as such can use all 4 or 8gb of RAM.

In view of this, using 2x4gb sticks with a 32bit OS is a waste of time and money. The maximum you should consider is 4gb.

Whilst on the subject of memory, you will note that the RAM for the M1330 is available two flavours DDR2-667 & DDR2-800 (667 and 800 Mhz I/O bus clock speed). Only ever buy the DDR2-667 as although the DDR2-800 will function ok, the motherboard will only use it at 667Mhz as this is a hardware maximum. So again save yourselve a bit of money and go for the cheaper stuff. 

Thanks for the excellent explanation! I had figured that's what the case would be. Maybe I'll have to upgrade to 64bit OS just for grins. The 1330 is my daily beast and gets quite a workout but it's already running 4gb.

And I totally agree with you about not buying RAM or other pieces/parts from Dell.

Cheers / Jim