My first piece of advice would be not to purchase RAM off of Ebay, I would purchase from a reputable retailer which will guarantee that the RAM they sell you will be compatible with your motherboard. Crucial
has a scan that you can run to determine the best type and quantity for your computer, they are also one of the most dependable manufacturers as well.
DDR 400 is PC-3200
DDR 333 is PC-2700
DDR 266 is PC-2100
These are all speed of the RAM which is compatible with your motherboard, PC-3200 being the fastest. Wikipedia
has a pretty clear explanation of this, give it a read.