6400 is the model sold in Canada and in the US business section of Dell.

E1505 is sold in the US home and Home businesses section.

I own this model. Very ncie laptop.

You can get XP in option when you choose it from the business section.

Vista is nice. Simetimes unstable, but we must give him a chance : as you said in your post, it is a new software. Having XP and Vista in dual-boot is the best actual option. XP is stable and fast, Vista is beautiful but a little bit unstable.

It is possible to install Vista later when you have XP. You can install it in dual-boot. I have a dual-boot with XP and Vista.

Upgrading in Vista isn't a priority since softwares are just beginning to be compatible with Vista. Maybe at the end of the year Vista will be a lot more popular.

Make sure to get an ATi Mobility Radeon X1400 if you want to have the best gaming potential. If you want to stay with the GMA950 ( if you want to get more battery life, this is the choice to make ), you should go with the E1405. Less heavy, easier to manipulate and carry, it is a nice computer.