Hello:
I dont believe your motherboard has a sata controller, therfore if you want to use sata drives you would also need to buy a PCI slot sata controller card to run & connect a sata drive too. They cost about $35.00
Personally I would suggest you get a Western Digital ATA 100/133 IDE with 16mb cache 7200 rpm of the size you desire
the minimal performance boost you would see from the Sata drive would not warrant the $35.00 controller card I my humble opinion (IMHO)
I would get a bigger and faster (large cache) IDE drive as spec'd above, get the combo DVD drive you speak of , you should have atleast one gig or ram that would help your speed more than the sata drive if you dont have at least one gig now ?????
you should also get a new power supply(PSU) if you plan to add the hard drive and add the dvd rom drive
if you are going to replace your existing cd/rw with the combo drive then you may not need a PSU, but Dell's are know for having very limited PSU's in them and they dont hold up well to upgrade of components or add-in's
I personally would spend the $50.00 and get a Fortron 450 watt unit