can I swap a amd 400 or 500 into my dell optiplex 200 mmx computer?

Possibly...it depends on what settings are available. The most important one would be the CPU voltage...if you can't set it to 2.2v (maybe 2.4v), you can't run a K6-2. At 2.4v, you'd be overvolting & there's no guarantee that your CPU will handle the increase. 2.8v (MMX voltage) will fry the K6-2 If your max FSB setting is 66mhz, the best you can do is 400mhz CPU using the "2.0x as 6.0x" multiplier trick...simply set the multiplier to 2.0x & the K6-2 will interpret it as 6.0x, so you'll be at 400mhz (6.0 x 66.67 mhz). If you can set the FSB to 75mhz, you can run a 450 CPU (6.0 x 75mhz). But ONLY if you can lower your CPU voltage to 2.2v...the MMX runs at 2.8v. Look into the cacheability of your motherboards chipset too...I see you have 128mb of RAM...most of the older socket 7 boards only cached 64mb...by exceeding that 64mb limit, you're actually hurting your performance. http://www.pcguide.com/ref/mbsys/cache/char_Cacheability.htm http://www.intel.com/design/chipsets/applnots/memory.htm http://www.makeitsimple.com/articles/ramguide/ramguidep6.htm