Can i use someone else's Snow Leopard boot disk to upgrade my mac?

No for possibly two reasons ... First, that's illegal as it's a violation of the Apple license agreement, and second, boot disks are locked to the system type they are delivered with. Ask your Dad instead how you can earn $29 doing some chores around the house, or let the word get out that for any holiday gifts in December that cash would be appreciated.

Since you're on Leopard today, you probaby know in wanting to move to Lion that Lion no longer has the Rosetta emulator and thus doesn't support anything with PowerPC code. That's surprised some, so just FYI.

And, quite frankly, you're not missing anything much staying with Leopard. The number of software updates for third party applications in particular necessitated by SL, let alone Lion, could make it more expensive than you think without adding very much extra by way of functionality.

Taken by the book, Lion cannot be installed without having SL running on your mac! The genuine Lion installer is an application, in fact a folder with some scripts directing towards a disk image within that folder, which contains the system proper. We are bound to refer to strictly legal aspects of the issue, though—