Yes. You can use a WAP (wireless access point) for this. You can also use a wireless router as a wireless access point by simply ignoring the WAN port and disabling the DHCP server. You'll find that wireless routers are cheaper than WAP's and also include a 4 port switch.
Yes. The wireless links are bridges. They know nothing about IP addresses. They act exactly as if they were ethernet extension cables.
With a wireless router, you can put them on a seperate network. However, that's neither necessary or something you would want to do.
Yep. That's about it.
Wrong. ADSL maximum speed is about 6Mbits/sec. Unless you're paying for this, you'll probably be rate capped at about 1.5Mbits/sec.
802.11g will do about 15-25Mbits/sec thruput at short (10ft) range. The speed will go down as the range increases. The wireless thruput is at least 10 times faster than what I'm guessing your ADSL connection will do. Unless you're operating at the extreme distance, are going through many walls, or have lots of multipath and interference, I wouldn't worry about the internet to wireless speed.Dunno. You haven't described the problem. What problem are you trying to solve? What do you have to work with? Where are you stuck?
W95, 98, ME, NT4, W2K, XP, WinCE, etc?