^^^ QFT.
I have a Pioneer AVIC F900BT, and it won't spin anything larger than about a 100GB 2.5" drive. I think most Pioneer units are like this.
You can get around that by using an external HDD that has an external power supply, but then you need provide that power with a converter.
Even if you do get it spinning and reading a larger HDD, expect long loading times on startup. It'll have to index the songs on the drive.
I agree with blackdragonaudi... get an iPod and call it a day, especially if your head unit supports iPod control. You won't regret it.