However, since you get to choose the exact configuration, how well it will run will vary. For instance, Vista needs 512MB RAM and prefers 1GB+, but you can order the E510 with just 256MB.
Aside from that, note that Vista is graphics-intensive, so you'll need to pick out a good graphics card if you want to take full advantage of the new interface. (The standard Radeon X300SE should handle the glass effect and such upon Vista's final release, but it will not be a high performer.
As to upgrading to Vista, all of the details have not been released. What is known is that you'll have the options of Vista Home Basic, Vista Home Premium, and Vista Ultimate. Home Premium is similar to XP Media Center Edition and is expected to retail for around the same price as XP Home, so $200 full and $100 upgrade. Vista Ultimate has no XP equivalent and prices are just speculation at this point, some saying around $500 while others saying closer to $300. At this time it's best to just make sure it's capable of handling Vista and considering upgrade paths when more information becomes available.
Hope this helps,