If you are running OSX 10.5.7 you cannot use iCloud on your Mac since one of the requirements is that the Mac needs to be running Lion. However, if you are really running 10.5.7 - you can't sync the iPad either since the minimum for that is 10.5.8.
I will assume that your tagline is incorrect and you can at least sync the iPad with your Mac. And .... you need to have Numbers installed on the iPad so I will assume that you have that installed as well.
The text below is copied from the kb article below.
Copying Numbers files from your computer to the iPad using iOS file sharing (Title changed for Numbers)
- Connect your iOS device to your computer using the included Dock Connector to USB cable.
- Open iTunes on your computer.
- Select your iOS device from the Devices section on the left side of iTunes.
- Click the Apps tab and scroll down to the bottom of the page.
Note: If you do not see the File Sharing section shown in the image below, your iOS device does not have any apps installed which support File Sharing, such as the iWork for iOS apps.
- Under the File Sharing section, you should find a list of apps currently installed on your iOS device that use File Sharing (such as Keynote, Pages, and Numbers for iOS). Select an app to view a list of the files associated with that app on your iOS device.
- You can drag and drop files into the Documents list to send them to the app on your iOS device. You can also click the Add button, locate the file or files you want to send from your computer, and then click the Choose. The files you select will be copied to the app on your iOS device immediately. Select only files that are supported by the iOS app. Once you’ve copied your file(s) to your iOS device from within iTunes, open Keynote, Pages, or Numbers on your iOS device.
- Navigate to the Document Manager screen
- Tap the plus icon in the upper-left corner, and then tap the iTunes icon:
- This will open the "Copy from iTunes" window:
- Tap the file you want to copy and the document will automatically be added to the Document Manager and open.
(Any compatible file that you’ve copied to your iOS device using File Sharing will be listed in the "Copy from iTunes" window. If the file is not listed, confirm its file type is compatible with the iWork app.)
Back to my own words now.... You can sync these documents to iCloud using your iPad as long as you set it up in the iCloud settings. If you make changes to this document on the iPad - it will not sync back to the Mac via iCloud. You can sign into your icloud.com account on the Mac - click on iWorks - click on Numbers - select the file - and download the file to the Mac to work on it again - but you can't upload it again unless you are running 10.7.2 on the Mac. You will have to get the file back onto the iPad via file sharing as described above.