Upgrade X3 Producer and questions about installing on disk D

You can install it on D, but you will very likely have some performance issues.  Not because it is on D, rather than C, but because you will be running programs and massive amounts of data on the same physical drive, and that will almost certainly cause things like dropouts, crackles, and such.
 
You can pick up a new 2 TB SATA III HDD for around $100 usd, or a 1 TB SATA III HDD for around $60 usd, these days, and this would be a HUGE beneficial thing you could do for yourself.
 
The generally followed setup for lots of folks is to have the OS and applications on the C drive, and data (sample libraries, Cakewalk Projects, etc.) on 1 or more additional physical drives.
 
If you are using a laptop and do not have the ability to add an internal drive, then you could add an external eSATA or USB drive, depending on available ports.  (eSATA would be the fastest, followed by USB 3, and lastly USB 2).  I suppose one could use a Firewire-connected drive, but I myself would choose a different option, as a personal choice.
 
Please add your system specifications, like you see at the bottom of my post, to your forum profile's signature/footer section.  
 
This will accomplish a couple of things.  Firstly, we can evaluate your system for its ability to run Sonar, and secondly, us knowing your environment helps us tailor our assistance to you for any issues you post.
 
Bob Bone