I am sorry, but I have to agree with the consensus that it might not be your HD. Constant beeps can be caused by a lot of things, and the most prominent that comes to me is a stuck key on your keyboard.
Your question about HD sizes, which version of Windows? I think anything below XP SP1 won't support more than a certain size with out an update (I think), but after that, the only limit is how many SATA or IDE ports you have.
We really wanna help you fix this, and we were just voicing our thoughts in the other thread. If you really want to buy a new HD, what is your price range and minimum size? I know you said Newegg and WD, so here is a really nice 500gb for 100 bucks:
http://www.newegg.com/Product/Produc...82E16822136185