First you need to look at what memory is installed already. It is usually accessible through a small cover on the bottom of the laptop, look this up in the manual. You will either have one 256MB module or two 256MB modules or one 512MB module installed. If you’re lucky you have one 512MB and can just add a second one.
Then look at the label on the installed module(s). Usually you can make out whether it’s PC2700 (333MHz) or PC3200 (400MHz) and get the same type.
BTW, I see the Satellite 2410 has an i-Link / IEEE1394 / FireWire (that’s all the same) connection on-board, so if you get the Plextor PX-740UF, you don’t need to buy a PC-Card to hook it up.