This is of topic, but can anyone tell me what is irongate chipset for Athlon?

in my pc i have 500 MHz athlon and motherbord supports up to 750 Mhz so i found on ebay 750 Mhz thunderbird for couple of bucks. But the guy says it need "irongate" chipset for it. I send same question to him but he haven't reply yet and auction will close soon. If anyone can provide any info i'll be very greatfull.