I split this thread out, so your question will get the attention it deserves. In the future, just post your question in a new thread, not piggybacked on someone elses.
You can just plug it in, on top of the existing drive - the cables are right there waiting for it :)
Remember to set the drive to slave, using the jumpers.
A single 1.25GHz processor? No, that should be an MDD 2003 model. Will not need a new ATA card to install a 200GB disk in there. You WILL however, have to put it on the same bus as the boot disk. That's the ATA/100 bus which will recognize greater then 128/137GB. The bays to the left of the chasis are ATA/66 and are limited to 128/137GB.