Can I use this Ram ?

Hello, My PC has a 512mb Ram, PC3200,DDR400 mhz.My mainboard manual says PC2100,DDR266mhz up to PC3200,DDR400 I just bought a new stick 512mb “via” Internet,and they sent me a PC4000,DDR500mhz. Now,will this work in my system at a lower value like the DDR400mhz or should I send it back. Thanks, Kenny