Hey Stop Start!
You have to start somewhere and fitting HDD is not a problem in itself as our friend
spanners says .
I have just fitted a new 80gb Maxtor 7200 and it went well. However, I doubt that your pooter will see two OS's when it boots. It will boot as before. But you have to install the new drive and it will take up as D drive. Better be careful here 'cos the Seagate installtion disc can easily format your C drive in the process!
You will have two drives - C will be your primary and your new drive will be D so it will boot from C. Still with me? C Drive will be the Master with the XP OS on it and you will have to set D drive as a slave with the jumps they give you.
I got a ATA card with mine and I don't use it, but when I did it dropped down to 100 from 133 and not the other way. In other words you don't HAVE to use it.
I would suggest that you install EVERYTHING before you even think about copying or such. But once settled in with the lot working well you can move anything over to C drive.
Why would you want to dispose of your old drive btw? It will make a great backup tool, which will duplicate your C drive if you want.
You can always mail me too.
Hope that helps.