Hi, I have a dell 8400 with 3ghz processor, 1gb ram and a 150 gb hard drive. I want to buy a new hard drive cos mine's nearly full, but I know stupidly litle about computers. I fancy one from ebuyer, but can I just slot in for eg a sata western digital 250 gb hard drive with 16mb cache? Will my oldish computer be compatible? Thanks if anyone can offer advice.