Huh? Sorry, but that's totally unclear.
What exactly are you trying to do? You can't turn CS3 into CS4 and you'll be hard pressed to buy a legitimate copy of CS4.
Sorry if it was unclear, I'll try to explain better.
I have CS3 (legitimately) on my laptop.
I started working at a company that installed CS4 on my desktop computer.
I understand that I can install an Adobe product on both a desktop and a
Can't I put the serial number into my existing CS3 to upgrade to CS4 or do I
really have to install the disks?
I'm worried that I'll have to remove CS3 before installing CS4 and I don't
want to do that in case something goes wrong, then I'll have nothing.
You'd need the installation disks and the serial number.
However, if the company has a volume license you would not be able to do this. Installing on two machines is for single licenses only.