Well said Knight Ewie.
But - Master Alpha. I recommend you take a look inside your pc. See which cables go where. Disconnect them - and conenct them. Seriously.
There is only ONE place where everything can go in...
Some tough stuff is jumpers and master/slave. You might want someone you know to help you with that - if you can't, I wouln't recommend it.
I don't know much about macs, but stop talking about Macs being virus free. If you want virus free - and do not want to pay a ****load of money, get linux. No viruses - and Linux's free. You got the same problem there though - gaming is hard. You can get jka to work with a program called wine(free) though. Linux has a lot in common with mac - execpt you have to know a few basic stuff to even get it running, which are completely diffrent from windows, but - there are very very complete "Switching from Windows to Linux for dummies" guides out there.
What I recommend, is simply, buying one part - replace it, check it works - buy another. If you are unsure about where things are in it, take out your cellular phone, and take a little picture of it.
If you want a laptop - buy Toshiba. You might say, but Dell is cheaper. Maybe - buy Toshiba IS more reliable. My farther has had his for 7 years I think now, and all that has been wrong with is, was a button was once stuck. My brother once had a Dell... Yeah he was okay with it, and it did last pretty long concidering he droped it down the stairs 3 times before the screen broke.
But yeah.. Since you're posting on a forum full of gamergeeks, I recon you want a pc you can also play on?
Windows XP Professional, which you buy your own parts for would be my personal choise in your place...