Yes, simply set up the second AP.

It was a common part of my testing at Microsoft to set up multiple access points on the same wired LAN.

The only thing you need to make sure of is:
- The two access points to not conflict in their wired addresses.
- The DHCP ranges doled out by the access points do not conflict. You might have to reduce the DHCP range of the WPA access point to leave room for DHCP addresses for the WEP access point.

If your cable modem already doles out all the addresses, it might be possible for the extra WEP access point to just get set to "Use existing DHCP server" in all cases and thus solve both of those two above problems automatically.


Oh, and:
- Remember to unplug the WEP access point when your niece leaves. The point of using WPA's additional security is completely lost when you've got that WEP access point plugged in.