Installing Windows 7 over XP

Hi,
I'm desperately trying to get windows 7 installed on my Acer 6292 laptop. I'm currently running XP Pro SP3 on it. I've tried everything I can think of but windows 7 won't boot from DVD or USB.
Just to get this straitened out first of all, my bios is set to boot in the following order USB then DVD then hard drive.
First I tried to make my USB bootable through the commad prompt. I found that to be impossible since my USB won't show on list disk command.
So then I tried the Windows 7 USB/DVD download tool. But still it doesn't work. When I try to boot from the USB it says ntldr is missing.
Please help!

Write ISO to flash stick using Universal USB Installer with Win7 in dropdown menu. Boot it using one-time BIOS boot menu key as stick can appear under USB, Removable or even HD's.

Set your BIOS to boot from HD first unless you don't have a one-time BIOS Boot Menu key..

If this fails, where did you get the WIn7 ISO? Confirm it's HASH or download another and try again.

You can also run the installation files from stick to install over XP from its desktop, but it would be best to get the stick booting so you can use it for repairs if Win7 fails to start, or if you replace HD.

Do you have an external USB hard drive you could use? Those work well also, and may appear where you USB flash drive doesn't...

Thanks Gregrocker!

There was something wrong with my ISO. Downloaded a new one and worked like a dream.