FAQ: Mac OS X Intel
Does Sketchpad work with the new Intel-based Macintoshes?
Sketchpad version 4.07 (and later) are Universal Binary applications that offer native performance on both Intel and PowerPC-based Macintoshes. While earlier versions of Sketchpad could be used with Intel-based Macintoshes transparently under Rosetta translation, we recommend the free update to version 4.07 for all users.
Sketchpad version 5.05 is an Intel-only application on the Macintosh and no longer supports PowerPC Macs.