I agree that the new drive is probably larger than the old one
What you need to do is download and install a ghosting software and have it ready. Casper XP is my personal favorite.
This is for the grandson to do for you:
Then set the new drive as a SLAVE and install it into the computer.Then Ghost copy the C drive onto the new drive. (Format and partition the new drive first)
After Ghosting the original C drive onto the new drive, take both drives out of the computer and set the old drive as the new SLAVE and the new drive as the MASTER (we're talking jumpers on the actual drive here)
Reinstall the drives into the computer in the new MASTER/SLAVE configuration and you are off and running.
If the new drive is at least twice the size of the old one, I would recommend that you ghost copy the entire old drive to the new one and only install the new one in the machine as a primary drive.
If you decide to reinstall the old drive with the (D E F partitions) the partitions will automatically change letters to E,F,G,H as the OS does that automatically. I am assuming you have a CD?DVD which will be assigned the D drive letter. Also, afterward, any program you open from the old drive will run from that drive and will continue to store data on that same old drive. That is why I recommend that you just ghost copy the entire old drive to the new one and then chuck it.