Several issues here!
The drive you mentioned is one of the quickest on the market, I think I am correct in saying it is the ATA133, 7200rpm model.
But your Gateway 366Celeron will probably only have a harddrive interface of ATA33 and will also probably have an issue recognising such a big drive.
Forgive me for saying probably in my comments but without some reseach (if the information is available) it is not possible to be absolutely sure.
At best there could be a bios flash on the Gateway website enabling this motherboard to recognise the new drive size.
In practise if the motherboard does recognise this drive it will just mean that it will be forced to run at the slower motherboard speed.
Buying this drive may make sense if you intend to upgrade your system at a later stage but a cheap ATA100 5,400rpm drive will run just as quick at the moment on this rig. Martin Please let members know if there advice has helped any.