Dual OS boot problem...HELP!?

I bought a used Toshiba laptop (ill have to add the exact model when I'm home later) and the man I bought it from had the computer on and when i tested it everything looked perfect. When i got home, i turned it on and ended up on a black boot screen that made me choose between MACOSX or Win7(this is the first problem....how do i delete the MacOSX from one partition, i have no idea how!!) . I chose Win7 and came to the log on screen and didnt have the pword and no guest option was available. Amazingly, he never answered the phone and hasnt to this day to help me with this. I got a copy of Win7 from a friend (burned to a cd) and tried popping it in and turning pc on...and the cd never loaded even after changing the order everything booted up in the boot options. I somehow ended up figuring out how to log on his original account by just typing pwords and put in win7 and basically started the set up. When i did the whole set-up it saved the old version of windows in a folder, I noticed this took up 90% of the disk space so I found the folder and deleted it. Ever since, I've had hard disk failing errors popping up on me and I cannot load the damn Win7 cd from boot to do a clean reinstall of windows (at least i cannot figure it out) someone help me! anything will help!!