Ethernet hub

So I am putting a desktop in my room with a pre existing xbox that has ethernet ran to it from the ceiling. I obviously want the desktop to have ethernet ran to it. My question to you guys is.. do I have to run an entirely new 50ft long ethernet cable through the ceiling again for this new device or can I use something a long the lines of this http://www.cellphonecases.com/Ethernet-Splitter-Adapter.html?utm_source=googleshopping&utm_medium=cpc&utm_campaign=productads&gclid=Cj0KEQjwvOC5BRCb_8yNmZ_ls9IBEiQACTz8vi6X35rs_JQ1w1MaJTHDlmhnr5iZk_tId2pLt2R0ROEaAtk18P8HAQ#.VzjORp8pDqA to split it between the two devices? If I am able to do this, how much slower should I expect both devices to be now that they are split? Will it be noticeable?