iCLOUD AND SNOW LEOPARD

Snow Leopard (OSX 10.6.x) and earlier systems are not compatible with iCloud: Lion 10.7.2 is the minimum requirement, Mountain Lion recommended.

You cannot create an iCloud account on Snow Leopard or earlier. If you have opened an iCloud account on a Lion/Mountain Lion Mac or an iOS5/6 device this will be the situation on Snow Leopard:

• You will be able to access email and calendars on the iCloud website at http://icloud.com provided your browser is reasonably up-to-date.
• You will not be able to sync contacts or bookmarks from a pre-Lion Mac.
• You will be able to enter the server settings for email manually in the Mail application and access your email. A pictorial instruction page on doing this is here (for Snow Leopard, or here for Tiger).
  
• You will not be able to sync your calendars directly.
• Some people have been able to set up calendar syncing by using the method detailed here - this is an unsupported hack and may not be reliable, and may stop working at some future point. (See below for alternatives.)
• Address Book won't sync: this page has a convoluted hack to make it sync which has been reported as working (and as not working by others). I've not tried it. (See below for an alternative.)
  

(Macs running Tiger can access Mail but will not be able to sync the other data.)

There are a couple of alternative syncing services you might like to consider, though they're not particularly cheap:

Soho Organizer can sync Calendars and Contacts with iCloud on Leopard, Snow Leopard and Lion. A single user licence (multiple machines allowed) is $99.99.

Fruux syncs Calendars, Tasks and Contacts beetween a wide variety of devices (not using the iCloud server) including Snow Leopard and above, Windows Outlook and Thunderbird, Linux Thunderbird, and iOS and Android devices - see their compatibility chart (click the blue 'i' for a caveat about Snow Leopard). It's free for one user, two shares, two devices; above that pricing starts at $20 per month.

(I have no connection with these firms and have not tried their products, though both have had good reports.)