If you don't have at least a Core2Duo MacBook, you won't be able to use iCloud in Mac OS X. A CoreDuo or CoreSolo MacBook is not compatible with 10.7. It is compatible though with Windows 7, which is compatible with iCloud. Some iCloud services work with pre-10.7.2 systems, but not all.
Rosetta is not compatible with 10.7. So you won't be able to run applications made for pre-2006 Macs.
That said, read these tips for upgrading to 10.7:
And getting iCloud
Some links on the iCloud tip that may be useful no longer work, so asking on the iCloud forum is probably best: