I guess you are talking about:
Ebay Viewsonics 4-way TV cable booster (should work with cable modem)
In my area, the cable system is supposed to provided just enough power to supply an 8-way passive splitter (I have that in my home--and it does work with analog TV and a cable modem). If split more than that, I can expect signal quality problems and problems with my cable modem.
If you have good signal quality, then an amplified splitter will give you the power to split a good quality signal into more lines.
If, you have a low/noisy signal, an amplifier will amplify the noise along with the signal. You probably will not be happy in this case--The only solution is to talk with your cable company about your signal quality.
If you want to try something--you can probably find a cheap amplifier at you nearby electronics outlet (or borrow one from a friend) and install it for a quick test.
-Bill
PS: One thing to note, there is still a -8db return path loss as these amplify signals only in one direction... So, if you have a cable modem with poor "upstream" data rates, then this unit will not help that problem... To "fix" a cable modem signal quality problem, your best bet is to move the cable modem as close to the cable input as possible (i.e., the first splitter connection point).
