Rumour has it that we are to start seeing 7.5 CD's in the mail this week or next. This release will require new activation codes and you will have to (groan) uninstall first then reinstall with 7.5. It's something to do with Windows Vista (which you aren't running anyway) and it's inability to install over a previous version. It is recommended that you back up all of your tables, charts, highlighting, labels, layouts, INI file and PMD files before you install. Your images should be fine as long as they're not in the Space Planning folder.
Even though this release is primarily a bug-fix-release there is one big fix that will compel you to upgrade.