Yes the latest version is compatible with the Lion however some of the Lion features such as Auto saving is not yet available in the product.
No this is not possible, MacDraft PE and Interiors are completely separate applications.
MacDraft PE 5.5.0 and above uses ATSUI text features of Mac OS X. ATSUI does not support these styles at the moment. When it does, MacDraft PE will make use of them.
When you double click on the document, the system looks for the application that created by it's signature , if there are more than one copy of the application, the system will launch the first one it encounters, which may not be the latest version. Remove all older versions of the application, renaming the application will not help.
There is an incompatibility issue with MacDraft PE versions prior to 5.5.2 and Panther version of Mac OS X (10.3). Users of version 5.5.0 and 5.5.1 can obtain a free update to fix this problem. Users of versions prior to 5.5.0 need to contact their local dealer or Microspot with regards to upgrading MacDraft PE to version 5.6.
1024 x 768