That app doesn't require speed... you can use VirtualPC and a copy of WindowsXP to run it on your iBook. That's what I did.
If you are just using it to look up words, the Mac has its own built in New Oxford American Dictionary. Just highlight a word and Ctrl or right click. It includes a thesaurus as well.
My CD-ROM is the Complete Oxford English Dictionary (20 volumes when printed out). I’ve tried using it with Virtual PC, but my understanding is that the copyright protections are at a level that prevent it from running on Virtual PC. I have an older iBook so I don’t have the intel chip. I was using Windows 98, but if it would work Virtual PC running XP, then I might give it a shot.