I would install Poser to the c: and do as Acadia says , a seperate runtime on another drive .

In win xp you can set a folder to be compressed by the operating system . It doesnt appear any different , the system compresses and decompresses on the fly. You can also compress your poser libraries to use the compressed file format in Poser. That will save heaps of room.

You can get a drive that is USB port connected , the size doesnt matter , the biggest you can afford.

I would look at doing a disk cleanup and archive off any older files not regularly used.  

60 mb with poser pz3 files is not enough. There is a python script in Poser to compress the libraries.