Hi,
I think i know your problem, i will tell you about it:
Don't put files on the main memory, That uses Ram,
I suggest you: do not use Cab files, they take much memory, and you cant store them om Storage card.
In Add/Remove Programs asks the program if you want to store it in the default folder. Click on No and set it as Storage card.
I hope this is enough infomation for you
EDIT:
You can use a program to install .cab files on SD