This is the RAM you need to update your Advent 4211 to 2GB RAM and it is so cheap!
Installing the RAM is very easy too. Just turn your notebook upside down, take out the battery and unscrew all the screws you see in the bottom of the case. Carefully lift off the case bottom (especially around the ports on either side) and you will see the RAM slot above some black tape (this holds the installed RAM). Slide the new RAM in at roughly 45 degrees until the clips either side click above it. If it does not fit in all the way adjust the angle until it does or it won't get recognised once you switch your Advent back on. There is a gap in the base of the RAM so there is only one way it will go in. Once you have done that put the bottom back on and the battery back in and that is that. A very cheap upgrade.
This RAM is also what you need to upgrade the MacBook. You get to the RAM compartment underneath the battery and there are a couple of screws to remove. See the Mac site for details on this. If you have two 512 RAM peices, you will need to buy two of the above to get 2GB. All very easy and one upgrade you should ALWAYS do!