I use a Asus EEE PC 901 with one 4GB SSD and one 8GB SSD with an installed Ubuntu Netbook Remix 10.04. Because the 4GB SSD is much faster then the 8GB SSD, I installed UNR on the 4 GB SSD and mounted the 8 GB SSD to the home directory. But now my space is very limited.
Thats the reason why I want to know how I can change the installation path of a program.
Apps tend to install themselves to several different places in the filesystem, it's generally not straightforward to install them somewhere other than the default (although though some will work fine if you shift them.
4GB should be enough for an Ubuntu install, assuming user data is not on the same partition. In the meantime it might be worth having a cleanup. Ditching old kernels will create 100MB of space per kernel, so that's a quick way to free a lot of space.
As >>outofstep mentioned, you could just mount an additional harddrive or partion as /usr or as /usr/share. Most programs install the major part of their installation in these locations.
(First obviously you have to mirror your /usr files to the new parttion to make sure everything will still be in place. But I'm certain you're familiar with that part.)
You seem to know what you want placed where. If so, at the cost of re-installation, why not simply repartition your SSDs, then place your various directories where you want them?
On a netbook, always consider using RAM disk for temporary stuff eg /tmp.
