You can, however, use the next-most-recent version of iWork apps (the "iWork 09" programs) and the new iWork 10 apps on the same computer. Both work fine.
If you're in the middle of a project and need to finish, buy a copy of iWork 09 off ebay or someplace, install it, and use those until you finish. Then get used to the new versions, because that's it going forward (and recent updates have been great!).