I've read that the prefilter sponges for the fluval edge will fit the aquaclears, although to be honest i just use part of an aquaclear media sponge that i cut a slit into and shoved the intake in. It isn't as pretty as the fluval edge prefilters, but it seems to work. They sell the fluval prefilters at my petsmart, so I'd imagine they'd be easy to find. You can google "fluval edge pre-filter sponge" to see what they look like.
What kind of filter do you have? I think the sponges you linked to are actually really big, maybe up to 6 inches, but I'm not positive about that.
A baffle is just something to keep the water from pouring out of the HOB filter into the water with too much force. You can either use an old soda bottle to deflect the water like this: http://www.bettafish.com/showthread.php?t=30139
or use a media sponge rubberbanded to the output area like lion mom did here: http://www.bettafish.com/showthread....+baffle&page=4
. I use the sponge baffle and just make sure the bottom edge of the sponge is touching the water.