Yes, it does mean it will support slower RAM too, yet to have your board run at maximum speed, go with the faster memory.
SOMETHING I OVERLOOKED:
There is something I overlooked though before.
If your old RAM chips already in the machine are one of the slower chip speeds, getting faster RAM to add to the amount already there will make the faster RAM slow down to the slower RAM chip's speed, so its not advisable, and is a waste of money in doing so if this is the case.
To find out (if you don't want to replace and just sell the RAM in already if its slower) what RAM speed the others are running to:
Download this program
This will tell you the RAM speed in already, and it may guide to to either get the slower RAM, which will be cheaper, but the motherboard won't run as fast as if you used the faster RAM it can support.
If you replaced them all with 2x512mb chips though running at PC3200 (not really that expensive to do), your system will be running at the speed it was capable of doing.
WHEN YOU LOAD THE PROGRAM:
To find out, simply run the program after installation, and go to Motherboard, and then click on SPD. Within the list it will tell you the RAM speed the chips are running at that are in at the moment.
I hope this helps