If you 'upgrade' every item you mentioned, it won't be an upgrade at all. Only the cabinet, floppy drive, keyboard, mouse and monitor are left
That said, it can be an interesting technical exercise to do a less drastic upgrade to your existing system.
1. Add more memory if you can find some EDO RAM.
2. Overclock your processor as much as your motherboard jumpers allow.
3. Your BIOS may have a 32GB or even an 8GB limit for the hard disk. That is as far as you can go without a BIOS flash.
4. Your motherboard probably does not have an AGP slot. Ask some second-hand computer sellers; you may be able to find an old PCI graphics card that's better than the existing one. Is it a SiS 6215 card with 1MB VRAM ?