You need to overwrite the Master Boot Record with generic boot code. Alternatively, you could wipe the entire disk clean or temporarily convert it to a logical drive. GParted boot up CD should allow you to do either of these options.
I use a commercial program called System Commander.
Also some OS installs will over write the initial boot up code - Windows, Solaris, etc. Most Linux distributions don't unless you tell them to.
What are you trying to install on the hard drive?
To get the GParted CD go to: