Is there a way to install FCPX without disabling FCP7 on the same computer so that both programs can be used?

Here is Apple's support doc on running both applications – with different solutions. Just to add that with respect to other programs in the FCS3 suite, Motion4 no longer works in Yosemite, Neither does the preference pane for Qmaster (although there are work-arounds, if you're interested.)

Russ

Hey Hank, Favor to ask: I have FCExpress and am trying to open a file created on it on Final Cut Pro X. It says I need xml version to do this - but FCE won't export XML. Frustrating. FCP 7 WILL export XML. Is there any way you'd be willing to open a FCE file with your FCP and then export it as XML and send back to me? I'm happy to paypal you money to do this. I don't want to have to buy a whole version of FCP 7 to do this simple task.

CCan't do it. The FCP7 machine has to be able to link to the media before it can export an XML version to go to 7toX.