Are you reading that model number off the monitor?
Whats the model of the actual computer box?
At 80GB you must have a PATA IDE connection for your drive. So go and buy the biggest IDE drive you can afford (prolly 400GB I think is where IDE maxes out, but I could be wrong).
Install drive as a slave, boot up, format the NEW drive, and hey preston, about 360GB of spare space.
If you want to replace your 80GB altogether you will end up needing to either reinstall your operating system (and applications etc), or using software like Ghost or Shadowprotect to backup then restore the whole system on the new drive.
BACKUP YOUR PHOTOS, MUSIC, MOVIES, DOCUMENTS AND OTHER IMPORTANT INFO BEFORE YOU BEGIN.
Wow thanks for the prompt response. And yes I did take details from the monitor.Info from "the box" is; HP Pavilion t720a; 7200rpm serial ATA HD; Intel Pent 4, processor 515, 2.93 ghz, 1mb L2 Cache, 533 mhz FSB, 90nm; 256 mb, 400mhz ddr sdram memory.
Mybad on the PATA - early SATAs were indeed 80GB and I just made an assumption that that wasn't that case.
With a mid size tower like that you should definitley have room for a second drive. Buy a 500GB, or 750GB, unless you really feel the need for a 1TB, though I see lots of comments of people having trouble with them (though I am sure they are a drop in the ocean of happy 1TB HDD owners).
Will pay to open your case and see what power connectors you have, and whether you need any adapter to power the drive you buy (e.g. you may only have molex power in the case, but need SATA style power for the drive).
While you're on the job, you'd do well to increase the amount of RAM. 256MB is not much these days. Consider increasing it to at least 1GB, or even 2GB. One or two of these would make a huge difference to your PC's performance.
Your motherboard has four memory slots and can take up to 4GB of RAM so you should have no issues installing another GB or two.