I recently posted a similar question. The answer that I got was to keep all of the programs etc. on the boot drive (the one with the OS on it) and use the second drive for files. That way, all editing and other resource-heavy tasks will be performed on the second drive, which you can keep clean and free of fragmentation and have a good environment for the programs to manipulate the files in. And as you said, you will have a seperate place to keep track of your music and other related files, and not lose stuff in the midst of your boot drive. You do not install any programs on the second drive, it's for files and cache folders etc. only. .
Many programs have cache folders etc. that go to a spot on your boot drive by default, but can be changed and reassigned. In that case, you should also move the cache folder(s) over to the second drive, where you can make them as large as you want (only limited by the size of the drive) and they will stay clean and free of the junk that can end up there when they are on the boot drive. However, you still don't want to make the cache folders overly large, that would be a waste and lead to fragmentation - check the documentation of the programs to determine the optimal cache folder sizes.
In my case, I purchased the fastest HDD (within reason) that I could get and made it my designated drive for music files, as well as for graphics files. There is plenty of room for both. I bought a WD Raptor 10,000 rpm SATA drive, it is expensive for a 74GB drive, but to me it is worth it. 74GB of dedicated space for files is still way more than enough, even with the graphics files, since there are no programs or anything else on there. I had considered putting a really big drive there - I could have purchased a 300GB 7,200 rpm drive for about the same price, or less, than my Raptor; but in the end I wanted the performance and really had no need for a drive as large as 300GB.
