I have my poser program installed in my main C drive.  I have external runtimes for my poser content and I have those on my partitioned "D" drive with a mirror copy of my runtimes on my external notebook hard drive in case my computer crashes. But I access my runtimes from D drive.

I don't know about installing and running the actual program from an external drive though.

To free up space, you might want to look into compressing your poser runtimes, and if you are inclined to save .pz3 files, which are HUGE, then you might want to compress those too and burn them to a DVD or CD.

"It is good to see ourselves as others see us. Try as we may, we are never
able to know ourselves fully as we are, especially the evil side of us.
This we can do only if we are not angry with our critics but will take in good
heart whatever they might have to say." - Ghandi