Hi Lanparty. There is no harm getting the www.lanparty-computers domain, but I agree with others regarding the fact that if your site gets popular, the owner of lanpartycomputers.com could create some headaches for you because most people just don`t naturally type the hyphen key if they read about something online. Many use Google when typing a name, which is good for you since your site will almostt surely pop up to the top.
For any site that takes credit cards or PayPal, I would recommend a dot com. Unless it is a charity (.org), people just expect a dot com in my opinion.
I would think a bit out of the box and use something much shorter. That will be better anyway. Something like LANpartyGear.com. Tell people what you are offering if possible.
Hope that helps,
Andrew Darlow, Consultant & Editor
The Imaging Buffet
Author, 301 Inkjet Tips and Techniques: An Essential Printing Resource for Photographers - InkjetTips.com