Nothing wrong with second hand CPU's if they work - they work.
First thing I would do is throw away the PC2100 ram and get some decent memory. The speed in which the cpu can communicate with the memory will have great effects on the computers ability to render - and infact do nearly everything. Your bus speed will currently be 2x133mhz and is capable of 2x200 mhz, you have the potential to increase memory throughput by 150%. Also get at least 512 idealy 1 gig. With this alone you will see worthwhile improvments in system speed.
Several editing systems now rely more on GPU acceleration as well, (well a few do) your graphics card is very old relative to the system, consider something more moden again this should improve the systems overall appearance of speed. Oh I have a Geforce 4 4200ti for sale if you want to make me an offer lol
First B/W semi pro music video in the bag! More to come.
Dual Athlon MP 2800+ 2 Gig DDR Ram Pinnacle Edition V6.1 pro 2xXL1s