An add-on to what travis said...
First off, you should NOT use 90.0.0.x.
That IP Space isn't in use NOW, but that doesn't mean it won't be in the future, and if/when it is, you will have a problem reaching things on that block.
To read more about that issue, check out this url:
http://www.cis.ohio-state.edu/cgi-bin/rfc/rfc1918.html
In any case, the space you should be using is in the following ranges:
10.0.0.0 - 10.255.255.255 (10/8 prefix)
172.16.0.0 - 172.31.255.255 (172.16/12 prefix)
192.168.0.0 - 192.168.255.255 (192.168/16 prefix)
Personally, I usually use 192.168.0.1 - 192.168.0.254 with a netmask of 255.255.255.0 - which will be efficient enough for you to have 254 computers on one network (probably much more than you will need), but if you will need more, you could use a netmask like: 255.255.254.0 (192.168.0.1 -> 192.168.1.254) or 255.255.252.0 (192.168.0.1 -> 192.168.3.254).
Also, I recommend using the linux box to share the connection instead of the windows box, as you will have more control with the linux firewall/nat than you will with windows "internet connection sharing", although either way should be robust enough for basic home use.