( not the leading edge of computing I know )
your processor is faster than mine. ive only a 2 GHz as you have a 2.4 GHz. actually i only paid $175 for the system with everything included. although ive updated my hard drive, dvd burners, video card, ram and monitor.
i wouldnt worry too much about the size of the drive. they are all pretty much the same height and width, with some being longer than others. any respectable site will have the dimensions available.
as coolcolors suggested.
looks like your computer does have ide connection and uses Ultra ATA/100 interface.
so you will need to make sure and you have a 40 pin/ 80 wire ide cable.
also i dont know how much ram you have installed but looks like your computer can handle up to 1 GB DDR SDRAM. ram is pretty cheap but make sure you get DDR and NOT DDR2 as they are not compatible. i would suggest getting one stick of 1 GB ram as apposed to getting 2x 512 mb sticks.
edit// looks like i might be getting more ram at these prices.