You can expect Vista to take longer to boot up the first 5-10 times you boot
it since it loads more of the OS then needed until it learns what files it
does not need to load at boot time.
Also SP1 boots faster then the RTM release and if you have super Fetch
enabled it will also boot faster.
My system used to take 4-5 minutes also and now after 45 seconds I can
connect to the internet.