UPGRADING MY HARD DRIVE

Clarifications

First, look at the specs on your computer and identify the largest capacity HDD your motherboard will support. Then, find a HDD to purchase that is no bigger than that. When you purchase a HDD, the manufacturer should supply a floppy disk (or you can download the tools from their site) which will have the capability of cloning the old HDD to the new HDD for you. You will need to physically install the new HDD as a slave to the old HDD, boot to the HDD floppy disk and tell it which option you want to do.

You probably have an IDE hard-drive.
You can use Macrium Reflect for 30days to clone your hard-drive.

http://www.macrium.com/download.asp

But I'd think any IDE/Parallel ATA drive would be fine.

You should be able to find out all sorts of stuff here:
(enter your model number on this page)
http://compaq.com/cpq-country/cpq_support.html

Full generic instructions:
HP and Compaq Desktop PCs - Installing or Replacing a Hard Drive
http://h10025.www1.hp.com/ewfrf/wc/document?lc=en&dlc=en&cc=us&docname=bph03429

You can do one of two things. Retain the existing HDD and fit a Slave with a PCI to SATA Controller Card or fit a Suitable PATA Slave if you have room in the case.

Ideally if your M'Board has a SATA Connector on it you could use an SATA HDD but if it doesn't have a SATA Connector you will need to fit a PCI to SATA Controller Card like the one shown here

http://www.newegg.com/Product/Product.aspx?Item=N82E16815124020

Then start the computer and load the Driver for the PCI to SATA Controller Card and when that is finished open the Drive Management and format the HDD. You can then start using that Slave Drive.

Col