Yep, completely safe.
1. Install a bitcoin client on the other PC (was thinking of MultiBit so as to eliminate block chain syncing)
2. Locate wallet.dat on the macbook
3. Copy wallet.dat to a usb drive
4. find the wallet.dat on the PC, rename it, and drop in the wallet.dat from the macbook.
Is that correct?
That's correct if you're going Bitcoin-Qt to Bitcoin-Qt. If you want to switch to a different client, you can either export your private keys from Bitcoin-Qt and import them into the other client, or send your Bitcoins from Bitcoin-Qt to an address generated by the new client.