Their emailed response to my inquiry about a Mac version for 2005 was:
Thank you for contacting H&R Block Customer Service.
We appreciate your interest in pre-ordering your TaxCut software for 2005. Unfortunately, TaxCut is not offering Macintosh-compatible desktop software for your 2005 taxes. We encourage you to try one of our Web-based online tax solutions at www.hrblock.com.
If you have further questions or concerns, please "reply" to this e-mail. H&R Block values you as a TaxCut customer and looks forward to serving as your tax and financial partner in the future.
H&R Block Customer Service Team
If you'd like, you can send some feedback to TaxCut using this URL. If you do, please be polite.