Just go to iCloud.com and log in (on your Mac).
I still have Snow Leopard on my iMac and it accesses just fine.
However, your Mac iCal events won't be there until you upgrade to Lion, but that'easy to resolve. What you will see is any calendars from your iDevice(s).
Because I am not on Lion yet, my iPad shows calendars synced thru iTunes from my Mac, as well as those on iCloud. If I were on Lion, those would be merged with iCloud.
My solution.
I changed the name of the iCloud "Home" and "Work" calendars that appear on my iMac to match existing calendars on my iMac and transferred the events from the "on my iMac" calendars to the renamed iCloud calendars. (just select the event and choose the iCloud calendar instead). Then I deleted the empty calendars.
Then I went into my iCloud via the Mac and shared (click the little "broadcast" icon by any calendar - may have to go into edit) those new calendars with my wife. I then went into my wife's iCloud, accepted the shared calendars and shared her iCloud "Home" and "Work" calendars with me..
I then went into iCal on my iPad and retargetted all my events from the Home and Work calendars onto the iCloud ones and deleted the originals when they were empty.
I also went back into my iCloud via the Mac and accepted my wife's shared Home and Work calendars.
We both retain other calendars with stuff the other doesn't care about.
Now, until I upgrade to Lion, my iMac calendars won't update, but I can easily access iCal in iCloud, it won't be overly aggravating - except the entering a password every time part.
Hope this helps.