^^DDR-1 566Mhz will most probably work on a system supporting DDR-400 at a reduced speed of 400Mhz....
Btw i have a couple of Hynix DDR-400 and Perx DDR-366 (256Mb sticks) for sale.. PM me ur contact no. if interested, i shall call u in evening after confirming the Brands and speed. (and also warranty if any)
Would be around rs. 300/350 each.