We did the Cape Horn trip on the HAL Ryndam in 2001. This did not include the Antartic, but we had a great time, and I would recommend this cruise to anyone who wants to see wild scenery and a different view. I would also recommend doing some reading about the ports and history of the area before you go, as HAL falls down in the area of good port lectures (exclusively shopping information) and natural history or other lectures.
Although an older book (and very biased about the native people) we found Cape Horn: The Story of the Cape Horn Region by Felix Riesenberg and William Briesemeister very interesting for the history of the Horn, with lots of stories about the explorers and old sailing ships. There are several other titles available through Amazon. Reading Joshua Slocum's book "Sailing Alone Around the World" again which includes his account of rounding the Horn was also great.
We love geography and maps, so we ordered and purchased marine maps of the entire route and keep track of our location using our GPS too. The ships maps were not nearly detailed enough for us, and we wanted to know exactly where we were all the time.
This is not a trip for those who want to lay out in the sun all the time. Due to going from moderate to very cold weather and then to the tropics, you will need more clothing than most cruises too. We went in November (early spring) and it was in the 30s around the Horn and in the 90s (with 100% humidity) in Rio.