It is entirely possible to enhance your signal from a Linksys N router. You are correct however, in assuming that you need the airport extreme to be able to use the Airport express. Therefore, you need a different type of range-extender that is compatible with Macs.
I currently use the Wi-Fire which attaches via a USB port and enhances the signal of any router since it is a directional range-extending antenna. Just point the antenna in the direction of your router (which can be located anywhere) and click connect in the connection manager. Its really quite a simple device and has the streamlined look/feel of using your normal Mac connection.
The adapter is made by a company called hField, and only costs around $60.
I hope this helps!
*(Computers: several Windows 7 computers and a Macbook running Snow Leopard)
I currently have a Linksys WRT160NL Wireless N router at home for my wireless internet needs. I want to be able to extend the range of the signal and heard that the Airport express can do this (I also heard it would only work with Airport Extreme), so is it possible to do this? If not, any other inexpensive ways to wirelessly extend the range of my Wifi? Thanks.