So I changed the subnet mask in my router, now I can not see the ssid broadcast. Any help?

I was messing around with the settings of the WRT54G and changed the subnet to 255.255.255.128 from the default of 255.255.255.0. How would I go about connecting to this to change the router back to the default? To add insult to injury the router is in my neighbor's apartment and she is not home. Yes, we split the bill.

Thanks! I know it was stupid.

Edit: currently on windows 7 and also have a ubuntu netbook if that makes it easier.