The last Dell machine I set up had SATA as opposed to IDE drives. This is an entirely different type of connection the former using round cables and the latter using flat ribbon cables. The power supplies could also be different. That said you can buy adapters to suit the old drive should you decide to add it as a slave drive to the new computer.
I presume you will have Vista on the new computer and if so you will; need to transfer your data using the Windows Easy Transfer Tool (WET) which replaced the XP Files and Settings Transfer tool. You can do this using an external Hard drive, DVD Discs or a cable connection. click here
Once the data is transferred you may need to check inside the new Dell and look for suitable IDE Ribbon Cables (there may be one)and power supply connectors similar to those on your old Hard Drive, so check those too.
Ideally you could run WET on the old drive and save the data file, which is compacted to the same drive. Move the drive and connect it to the new system and extract the files to the new system. Then wipe the old drive (Reformat it) and use it to store your music or other data.
Your best bet is to post back when you`ve had a look inside the new box and we`ll talk you through each stage.