Needing some advice/help with Vista

For starters I got this computer (Just the tower+monitor) from a friend earlier today.
I am trying to erase Vista and install a fresh copy of 7 Ultimate over it.
1. I can’t boot from CD. (Even with the BIOs tweaked, still goes straight to loading the HDD.)
2. I can’t upgrade the OS. (Says theres not enough space, when theres about 156GB left..)
3. I can’t run the Advanced Install (Says my “Drives/Drivers” can’t be found to access my HDD.) Error message – To install the device driver needed to access your hard drive, insert the installation media containing the driver files, and then click OK. Anyone have any ideas on how to fix this? I just got the internet up and running on this thing and it’s really starting to aggrivate the hell out of me.
Any help/ideas I’m willing to try anything.
Answer #1
Did you save the settings in the BIOS?
Answer #2
Try to get a Windows CD with HDD Integrated drivers.
The best way for this, would be, to create a CD of Windows with the drivers of your hdd.
For example, You take a .iso of win Vista, then You edit the windows by integrating your HDD Drivers, and then You burn the ISO to a CD.
BUT FIND THE RIGHT DRIVERS FOR THE HDD!