I've been wanting to jump into the Mac scene for awhile now, and these new iMacs are exactly the excuse I've been needing to force myself to do it. An iMac with a dual-core Intel chip? Man, two years ago that would have been unthinkable.
I've got an Ipaq 5550 and it can be a pain in the butt to get it going at first. Are you connecting to an access point or router that has security enabled? Make sure you have the latest firmware for your card so you can connect with WPA if needed.