16gb, never go to small. This way when you upgrade you have plenty of space. But 8gb will work fine. 4gb may not be enough.
as the title states, what should I get. 2, 4, 8 or 16 gb.
ummmm.... you dont need that much. Since teh CF card has a limited number of writes get a 2 GB CF, use NLite to get windows install to like 1 gig or 700MB, then install centrafuse.. Then.. get a 2.5" SATA HD or IDE HD, and use that for music, video, and other stuff. That way it will boot up the Win XP and Centrafuse. You will then have more storage space for music and stuff, while not having to write to the CF all the time, making it last longer. 2GB should be sufficent, maybe 4 if you have a separate GPS program...
i was thinking of centrafuse. CEntrafuse is great w/ Iguidance. Still working on traffic updates through phone. THe XM way is still by far, bar none the easiest and most reliable!