You do not have to have Windows to play online poker. Most major poker sites offer some sort of OSX-compatible software, even if it is browser-based. Online poker software will most likely run on old MacBook/iBook/iMac. Unlike modern computer games, poker software does not require a lot of resources and the minimum requirements are usually low. There are some exceptions, such as the graphically-intense PKR Poker. You will probably not have to dual-boot Windows to play online poker but that is an option if there’s a Windows-only poker client that you really want to play. You can dual-boot any Macintosh computer with OSX Leopard 10.5. Most of the time the Apple software is identical to the original Windows version. There will be a few minor interface changes. Browser-based or “instant play” online poker sites means you can play right away in your web browser (such as Firefox, Chrome, Safari or Internet Explorer) without having to download anything. The benefit is that you can start playing right away. The downside is that browser-based sites are usually missing a number of the features that full clients offer (multi-tabling is generally quite difficult).