How would you build to give maximum upgradeability?

I was thinking:

Socket 939 AMD Sli-ready mobo
Get RAM in 1GB sticks.

If I was gonna buy one card now, and bump up to SLI in 6 months, would you recommend getting a 6800 Ultra, or waiting for the 7800?

Mark.

939 is a must

SLI is optional ... depends on your moneybag ... but its for sure no must in future

1gig of memory is even today more then enough for 99% of all normal PC users ...
better get 2 good 512MB chips in dual channel then wasting money now for 2gig modules (which can be cheap but the performance is bad)
and when 1gig is no longer enough there is already DDR2 out where you can buy 2x1gig then

A8N-SLi Premium? I like the heatpipe for the chipset, and is overall good board. I have NO plans to overclock.

I also like the new Zalman 9500. Looks like it will be the best air-based heatsink for some time.

In terms if RAM, I'm thinking of upgradeability. If I get 2GB (4x512), and then want to upgrade, I'll have to get rid of at least 2 DIMMS to make way for 1GB ones.

I won't be able to get DDR2 without a new mobo will I, as AMD don't support it yet?

Mark.

Hold on... so it's better to get 2x512mb ddr sticks than just 1gb ddr stick? and also isn't ddr2 actually performing margenaly LESS than ddr...

it does now ....
but corsair is already out with DDR2 800 and this is the point where DDR2 gets really interesting ... it just needs some more time ... but if you watch AMDs roadmap you will see that DDR2 is on the way
but there is no reason to wait for it ... just go for DDR1