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first of all i want to know whether its possible to play online with two xboxes and one computer?
Yes. Up to 255 Xboxes on one engine.
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Which one is better for that purpose? Xlink kai or xbc.
Xbc is shareware and NOT free on this area - atleast it wasn't the last time I checked.
XLink is freeware.
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what kind of wires do i need and how does the setup look like?
You need this cable:

Found here:
Patch cables on eBay
Your setup will be one cable from the pc to the switch, then one cable from the switch to each Xbox.
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what about the ips? static or dynamic.
Which ever you prefere.
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Because when I connected the box with the laptop via cable and I went online (wireless) everything was fine and worked great. Any ideas?
Which router and wlan adapter?
You can "2 nic" it; Access point -wireless- laptop -wired- Xbox