http://www.linuxiso.org/viewdoc.php/verifyiso.html - has info on how to verify that your downloaded cd image is ok
http://www.linuxiso.org/viewdoc.php/howtoburn.html - has info on burning your cd
The boot process will not interfere with your BIOS - all you need to do is make sure that your pc is set to boot from CD.
If you have a recent graphics card and pleanty of memory, you may as well go with the graphical install. It's easy to use and looks good. If your pc is lower spec, or you get problems with the graphical install, try the text install - it's the same as the graphical one, just less pretty
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