IP address of host of Wi-Fi ad-hoc network?

It could be that Windows is using APIPA, so you could try an IP in the range of 169.254.0.1 to 169.254.255.254 (169.254.0.0/16). That tends to be what (from my experience) Windows uses in ad-hoc networks.

The easiest thing you can do is go to the command prompt and type ipconfig.

Now, take a look at both your wireless's IP and subnet mask. You should see a section similar to this:

 Wireless LAN adapter Wireless Network Connection:

   Connection-specific DNS Suffix  . :
   IPv4 Address. . . . . . . . . . . : 192.168.0.9
   Subnet Mask . . . . . . . . . . . : 255.255.255.0
   Default Gateway . . . . . . . . . : 192.168.0.1

You want to take a look at the line IPv4 Address. In this example, the host is 192.168.0.9

If running out of options, try to look at the Address Resolution Protocol (ARP) cache: arp -a or arp -a -v for verbose mode.

Then match the MAC address with the interface you're after. You can get the list of MAC addresses on your machine with ipconfig /all.