Software Update Install Directory?

Hello:

I’m using the latest version of Avast! Free, including the software updater that comes with it. On my computer, I have the following drive setup:

C: = SSD(120GB) Used for my OS
D: = HDD (1TB) Used for Program Files, User Folder

Then I have other HDDs for other stuff.

Avast! is installed on my D drive. However, the software updater just installs programs automatically when I click the ‘Update’ button without allowing me to customize the directory. It appears that programs are installing onto my SSD when I want it to install on my HDD. I tried looking in Avast! settings to see if I can change this, but I didn’t find anything.

What can I do to set Avast to D as my default install directory for the software updater?

How exactly is your setup achieved? Links on the system partitions or…? Which ones?
What particular program are installed elsewhere?