Help needed to learn...

[forcerip]

I have a subbed CC sb5100 modem at home. I also got another sb5101 with me and my girlfriend wants to test it but somebody told me she has to be 25 miles away from me inorder to get 5101 working coz we might be on the same node. Btw my girlfriend lives like 10 mins away from me. Just a few noob questions;
1) I just want to know how much area does a single node cover?
2) Is there any way that both cm can be used simultaneously incase if we are on same node?
3) Any options?

Thanks to all who helped me so far.
Thanks