For 200$ dont think it will be done. Of course this depends on what you have on hand.
Taking a 939 motherboard with a 1.8 gihertz Winchester AMD,and 512MB of Ram,80Gb hardrive,Pwr and Case ,Operating System Software will set you back at ...minimum 550$
You would have a longer upgrade path with this.
Taking the XP type boards your looking at the Socket 462s ...
462 MB (Nvidia2 min ,or Via Chipset),Sempron (whatever speed-there are plenty to choose from to about 100+),512MB DDR Ram (check type- older ram sometimes cost same as new DDR400 for example),Pwr and Case,Operating System Software will set you back for ....340.00 minimum....
Taking a AMD 754 you still consider the RAM,Case/Pwer Supply Operating System software will cost the same (depending on what you choose be sure the pin count is correct on pwr/case combinations)...is a minimum of 400$...
You can query online proprieties at retail for example : Newegg.com (wwws if you want to go)...query 462,.754,.939 for processors,motherboards to see a list of products/prices. Same can be done with memory types,cases. In all instances though,the Operating System software can be less expensive if you purchase it with your purchase,since you can take an OEM price at the vendor. Using an XP HomeE upgrade can save you some bucks as well if while you are building your system you can use the old full version disk to install it. Not sure if XPHome is available in OEM.
Make a list based on the parts you have chosen for the processor type you have chosen. Check the cost.Making sure that equipment is compatable while your at it.
The monitor/display I did not include to the suggestion.But you might find a cheapy CRT for less than 100$ (search for them too). Then upgrade it later.
Wont do this for 200$.Unless you already have some compatible hardware wich can work with the motherboard...keyboard,mouse (PS/2),monitor (svga),video card(AGP,PCIe,PCI)...
Nvidia2 Chipset(AMD 462) with Sempron is a good starter combination.
ATIs RS480M2 (AMD 939) with Winchester 1.8 is also a good starter,since its onboard video is usable ,and wont have to buy a video card.Will be upgradable to most versions of AMD top of the line processors. It also has lan onboard wich is a must.And is a m-atx board.