can't able to change my OS

I made a great mistake by changing my OS to Windows 8. Since my Ram is too low, i cant able to work under windows 8. So i wanted to change my OS and downloaded windows xp sp3 32 bit. I made Hp pendrive bootable using a software named Rufus and tried to boot it but my system boots to windows 8 itself. I tried to change the boot priority and no use still it boots to 8 itself. And then i deleted Windows 8 , changed boot priority to bootable pendrive and it says no operating system available. Wat is the problem ? Why my lap not recognizing any bootable medium?
I have Acer aspire laptop, 128 GB HD and 2 GB RAM.
P.S I even tried to boot with windows 7 CD but still my lap doesn't recognise it and boots to windows 8. Only OS it recognized other than Windows 8 was Ubuntu 10.2 CD

 

You have to change the boot sequence so that the CD/DVD drive and/or USB storage is ahead of the hard drive.

To do so, completely turn off the computer. Power it back up and immediately press the Delete key or F2 key to enter the BIOS. Then go into the boot sequence and change the boot order.

You say that your computer doesn't have enough RAM for Windows 8. Actually, it does for the 32-bit version. I'm currently dual booting with Windows 8.1 Preview and Windows XP Professional on a laptop with 2 GB of RAM and an 80 GB hard drive which I partitioned into two 40 GB drives.