What's best way to deal with modem and computer being located in different (distant) rooms?

[iMore Question]

My computer (2011 iMac 27") is at one end of the house, Motorola modem (SBG6580) at the other end, way too far for ethernet cable. I just bought an Airport Extreme and have an old Express. I'd like to use the Extreme as base station, hook up external hard drive and printer to it, use the Express as input to stereo for iTunes. Aside from presumed slow internet, any problems with this plan? Suggestions for improvement? Thanks.

 

[kch50428]

A cable run of 100 meters/300 feet isn't enough?