Yes, you can have the software installed concurrrently. You may run into a few issues, as I did when going back and forth between InDesign 5.5 and 6. They may have fixed it, but the 2 apps were sharing a resource file and as each overwrote it after use, the next program to use it might not recognize it and tell you you have to register. Annoying but not insurmountable. Otherwise should be fine.
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