The Facts
The standard category five ethernet cable works on the Xbox 360, according to the Xbox 360 support website. Category five cables are used on the Xbox 360 because it has a 10/100 ethernet networking card.
Considerations
Almost all versions of the Xbox 360 come with an ethernet cord bundled in the package, according to Microsoft.
Tip
Microsoft suggests using a router with ethernet ports because directly connecting an ethernet cord from the modem to the Xbox gets tiresome. You would need to unplug the cord every time you want to use internet.