visually shrink a TAB

Hi,
I have fucking colllegues using DreamweaverMX _and_ tabulations to indent 
PHP/HTML code.
They recommend (oblige!) me using 2 Tabs / indentation (what a shit).
I almost got fired when I replaced the 4k-lines file's tabs with 4-spaces.
They just overwrote my work with a backup file and told me to do it again, 
with their fucking double-tab.
So... My only salvation is to make Quanta displays a tab less wide than the 
default "out of the box" settings.
My wish is to make 1 tab displays like 2 spaces.
I would like to affect only display and not file content.
Is it possible? How?
Thank you.