Trouble installing W7 on MacBook Pro

Hey,
I am having major difficulties installing Windows 7 on my MacBook Pro (early 2011). I had an option of getting either a download copy of W7 for free or a mail order for about $25. I looked at guides and they said a CD with an ISO image of W7 will work. So I bought a copy of Windows 7 with Service Pack 1 64-bit on my Macbook Pro. However, in order to download it, I needed to download it on a Windows machine. So I used my Dell Latitude D630. After it finished downloading, I copied the ISO image to a flash drive and transferred it to my Macbook Pro. I tried burning the image to a Samsung Pleomax 16X DVD -R but it said there was a problem towards the end. I opened the CD in Finder and I saw that it had the same file size as the original which made me think it should still work. I opened BootCamp and partitioned my drive 100Gb for W7. When it asked me to put in the disc, it kept saying it didn't recognize the CD. I also saw that it said I'll need "an authentic installation disc for Windows 7 Home Premium, Professional, or Ultimate". Then I tried putting in the Windows XP disc that came with my Dell Latitude. I did this before on my brother's Macbook (early 2008) and it worked without any problems. This time however, it gave me the same message that it couldn't recognize the installation disc. I am really confused as to what the problem is. Do I need an authentic disc? If so, can I get one for free since I already have the license key? Or is the CD I trying burning the image too not suitable for installing W7? If so, which CDs will work? Sorry for the long post, I'm just having a lot of trouble with this.