You might not need filters.
Read this for a better understanding of X10 foibles:
http://jvde.us/x10_troubleshooting.htmIf you intend on remote controlling "a bunch 'o stuff" in your house, you might invest in a good repeater (XTB IIR or ACT 234) before spending money on filters which may not be needed. As side note: appliances with switching power supplies are big noise generators (computers, "power bricks" for note book computers and other assorted appliances, microwave ovens, TVs, cell phone chargers, CFL bulbs, etc). However most switching power supplies, although noisy, do not interfere with the X10 signals on your homes wiring.
One thing to remember: unless you only got a couple of Lamp Modules and a Maxi Contoller, don't expect your system to be "Plug-N-Play", but its fun once you get it working.