2GB for Vista Ultimate is enough.

My Vista boot up faster than XP after installing all the apps. If you compared fresh XP with fresh VISTA, XP will be faster a bit. However, once you installed up all the neccessary apps, VISTA doesn't decrease in speed as much as XP.

One of the factor that slow down my XP bootup is the 3rd party firewall (Sunbelt)....in Vista i dun need 3rd party firewall coz the built in one already handle incoming and outgoing traffic (unlike XP firewall which only checks incoming traffic).