Well, some of those will be easy, some of those won't be so easy.
The 360 doesn't have a calendar or email really, so you can use something like Google Calendar for the rest.
Email can again be done via an online mail system like Gmail. This would tie in particularly well if you get a Blackberry or Android phone next time around with your VZW upgrade. And while relations between Apple and Google have cooled considerably, you can still access Gmail on an iPhone/iPod Touch via standard POP3 or IMAP.
Music and photos I would store on a NAS device. You can also store files you want to share among systems on that. Alternate you could turn an old system into a file server, but a NAS device would save you a lot of money in electricity bills.
Games you're just kind of screwed on I'm afraid. No real method of sharing those. Game saves maybe, not the games themselves.
And as for the Mac or PC decision... If gaming is involved, go PC, even though you can dual boot on Macs now, it's likely going to prove annoying. But since you have a 360, I suspect you won't be doing a lot of gaming on the computer, so then I would say it comes down to whether or not you have any programs that you absolutely have to have, and are they Windows specific? If not, then there's a lot of good things to be said about Macs. Just make sure you do your homework before buying to make sure you really understand what you're getting into with a Mac. And if you do get a Mac, be SURE you get the AppleCare plan. Trust me, speaking as an Apple certified repair tech, everything except the Mac Pro (which is a joy) is a real PITA to work on. For anything but a RAM upgrade with the iMac, you'll have to take off the glass (which is untempered and requires special suction cups to get off), front bezel, AND the display. The Mac Mini requires you pry it open with a putty knife, and the MacBooks have some very odd screws. The new unibody MacBook Pros aren't bad, so long as you are very careful around the batteries. The AppleCare prices are dirt cheap for what they cover, and that includes someone like me to work on them instead of you.
I have MacBook Pro, Dell notebook, iTouch and xbox 360. I would like to sycn calendars, email, music, photos, games etc. I am on Verizon and will be up for renewal. How can I sync everything together including a new phone? Any ideas? My brother swears by the Xbox live system and hates itunes. he doesn't own a touch or ipod or Mac. I own all of the above and would like to incorporate the best of them together. Additionally, we will be getting a new PC in the very near future and haven't decided on another Mac or Windows based system. I'm open to any ideas and suggestions.