You can keep version 7 and still install version 8 on the same system, Take. In fact, until you're sure version 8 will run and is stable on your system, it's probably a good idea to keep version 7 around.
You can open version 7 projects in version 8 -- but, once you do, you will not be able to open them with version 7 again.
I have several movies and stills installed on a different hard drive and am wondering if I uninstall the old whether I will loose this old data.
Uninstalling any version of PE will not affect any of your data files.
As a precaution to 'Murphy's Law', it is always recommended that you off-load or archive any important data/project files (in other words, back up your important stuff), before taking any radical steps, or major changes to workflow.
One way to preserve Project details is by way of "Save As" from the File Menu, then save all Project setting to another Drive/Location. This should give you two (2) iterations of the same Project (where one could be opened in PE8, saving the other for version 7)...
Good to know that PrE 8 can open and work with PrE 7 .PREL's. Going in this direction is usually pretty much a given, though not always. Going backward, is usually not going to work. Steve's advice is good.
I'm a big proponent of finishing any Project in the version, in which it was started, and then working with new Projects in the new version.
A shakedown of the new version is also a great idea. Each newer version has slightly different requirements, and most require a few more resources, because of their increased power. That an older version runs perfectly on one's system, is not a 100% guarantee that the newer one will function as perfectly.
Thanks to you all for the prompt reply
thank you for your advice
thanks for the advice.