There is little you can do to bring it up to today's standards. I wouldn't even try using that 4400 tower enclosure for modern components.
Your best bet is consider purchasing a new or newer used computer or consider the purchase of components to build your
own computer. Motherboard, Processor, Video Card, RAM, Hard Drive, Optical drive, PSU, New Tower, Operating System etc. All those
components have changed considerably since the days of that old Dell.
Do you plan on running Windows 7 or newer?
That Dell is an older Win XP machine. You posted in the Windows 10 Support section. A mod may relocate this to the appropriate area.
Edited by saw101, 17 September 2015 - 07:30 PM.