Im baffled from advice from your IT guy ! Assuming its the HD thats causing the crash, mirroring wont in any help. Mirroring simply duplicates all data, so if 1 HD dies, you have a 2nd copy so no data lost. If you mirror to a new HD thats say 500g, it will only be able to use 37.2g, ignoring the other 462gb.
If you plan to upgrade then forget looking for a IDE HD because all new MOBOs are SATA and the trend is not to even supply a single IDE slot. IDE is slower anyway.
Buy a SATA drive and use a dongle like this http://www.usbnow.co.uk/Adapters_&_Connectors-SATA_to_IDE_Adapters/c42_45/p146/SATA_to_IDE_Dongle/product_info.html
You can buy cards for about £30 that will give you 2 or 4 SATA ports.
Or consider a USB external HD ( much slower ), but whatever your long term plans, if it is the HD at fault, copy the data off quick as it will die any second and you lost it all.
Forget this cloning/mirroring nonsense