Your signature says you are running 10.6.8 - is this correct? You cannot use iCloud to sync your calendars unless a) you are able to set it up on a Mac running Lion or above, or an iPhone running iOS5 or above; and b) you can get the unsupported hack described here to work.
You may be able to sync your Macs with Google calendar: that's something you would need to investigate on their Help pages.
There is a third party solution, though it's not 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.
If you can upgrade your Macs to Lion or Mountain Lion you would be able to make use of iCloud. You can purchase and download Mountain Lion from the Mac App Store; you can purchase Lion by ringing the number at bottom left of this page.
Requirements for Lion:
- Mac computer with an Intel Core 2 Duo, Core i3, Core i5, Core i7, or Xeon processor
- 2GB of memory
- OS X v10.6.6 or later (v10.6.8 recommended)
- 7GB of available space
The requirements for Mountain Lion are listed here: