I login via SSH to my host, using SecureCRT and use the tar app that most systems have
z (gzip)
x (extract)
v (i forgot)
f (i forgot)
But its alot better to use this method vs winzip, or the likes, if you do use a windows based extractor I'd use winrar. However you should be able to just dumpt he contents of the tar ball into the root of your x-cart install.
OR use a control panel system (if your host has one) that will allow you to extract on the server.
hth.