The best and fastest method is to install the new IDE drive on the second IDE channel as IDE can only access one drive at a time per channel but can access both channels simultaneously. Use Ghost (or my favorite Drive Image Pro by Power Quest) and transfer the contents from one drive to the other and extend the partion on the second drive during the transfer, but remember NT doens't do well booting to system partitions larger than 7.8Gig. (You can exceed this, but I've seen this come back to haunt me later even with Apps like Server Magic) so just create a second partition with the disk administrator later to use the remaining drive space.
Then of course just swap the drives around so you now have the new drive as primary.
Since youare not using any fault tolerance and are running IDE as a system drive, I'd suggest purchasing a third party IDE RAID controller and mirroring you OS drive.
Try this one:
http://www.ars-technica.com/reviews/4q99/fasttrak66/fasttrak66-1.html