kabir2, Duron, SDRAM, cheap, and complete system ... that boils down to using a PC-Chips M810LMR or M841LR.
These are all-in-ones with 3D VGA, decent sound, 10/100 LAN and AMR modem. 810LMR uses the older SiS 730S
chipset and has an AGP slot for future improvements on the graphics, while 841LR has the faster graphics
SiS 740, no AGP slot, and can run either SDRAM or DDR. They're both MicroATX and fit into neat small cases.
If you want to use separate graphics, I second the recommendation of K7S5A (aka M830LR). Get the version with
LAN to have your parents ready for fast internet.
http://www.pcchips.com.tw/M810LMR.html
http://www.pcchips.com.tw/M841LR.html
http://www.pcchips.com.tw/M830LR.html
Don't expect too much end user support from that group of companies though. Know your stuff, be sure all you need
is a manual, drivers and BIOS updates - because that's all there is.
regards, Peter