Yeah no reason not to just buy the Free McBoot card when you're using a Slim. With a fat PS2 it's easy to make a Free McBoot memory card if you have a hard drive adapter and a drive. Then you could just install Free HD Boot from PC to the hard drive and from that make a Free McBoot memory card on the PS2 (it's actually a lot faster booting from the memory card than from the hard drive).