Set it to boot first to the DVD and then to the HDD as second device. Also make sure you actually have a DVD drive on that computer, since if it's a CD, it will not run the DVD and will default to the HDD. I suspect that is your problem.
What size is this hard drive? 40 GB? If so, you couldn't run W7 very long on that anyway.
Give Lubuntu a try. It can boot from CD, is currently supported, and a 40 GB HDD isn't too small for it, if you choose to install. You can try it out fully before install, but can't save anything from CD since that's "read only", but otherwise will run entirely from CD.
Give this a try. Download this ISO file and "burn image" to a CD writeable disc. Boot to it.
If anyone has had this problem and/or knows a solution it would be greatly appreciated! I'm losing my mind trying to figure it out!
I have an old Dell Dimension 3000 with Windowns XP and I'm trying to upgrade to Windows 7. I've tried to install it with a bootable DVD but XP just starts up as usual, I've also tried 2 different bootable flash drives, on start up, I hit F12 and change boot sequence to USB Flash Drive, that seems to do something as a loading files screen appears but once loading completes, XP just starts up again as normal and no Windows 7 installation screen appear!
Anything obvious I'm doing wrong here? As I'm quite a novice at this sort of thing!