Installing Qt 5 and Qt 4.8.4 in the same PC
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Yes that is possible, i have the Nokia's sdk and Qt 5 on two Windows systems and on one i have an additional static build of Qt 4.8.1.
You just install (or build) it in separate folders and then configure in Creator the "targets":http://doc.qt.digia.com/qtcreator-2.4/creator-build-settings.html (or the "kits":http://doc-snapshot.qt-project.org/qtcreator-2.6/creator-targets.html depending on the version of Qt Creator you use) for each Qt version.