Dual channel vs single?

[UltimateBlob]

I'm planning to upgrade to a system with a Q9450, but I want to keep WinXP (32-bit) for now. This means I can only have < 2-3GB RAM, right? Well, that's fine for now, but in the future (say a year or two) I'm likely to upgrade to Vista-64. The motherboard will support up to 8GB (4 slots). So my question is, how much better is dual channel mode vs single? and is it worth getting 2x1GB RAM or just 1x2GB (seeing as there's little difference in price)? 'cause it's possible that at some point I might want to upgrade to the full 8GB and don't want to have to sell the RAM.

Also, is the performance boost on 64-bit noticeable with most apps? I read that when in 32-bit mode, the Core2s close off half their processor pipes (or whatever) to save power, meaning they're only half as powerful (?).

 

[uv]

The cores don't close off pipes, as it were - they just process smaller chunks at once

tbh, even if you're using a 32bit operating system, I'd grab 4GB of ram - it's so cheap nowadays, you'll get the large benefit from dual channel, and the OS will see ~3.5GB of it until you upgrade the OS.

*edit*

and welcome to the forum