Wireless repeater blues

I am looking for a good way to install a wireless repeater (the SysLink I purchased was a complete dud, and this is confirmed by several people on the internet).
Here is my problem: On the 1st floor of my house I have a wireless unit set up, which has a WEP password and can be used throughout most of the house by anyone who comes in, provided they type in the WEP password. No problem.
But it does not reach the corner rooms on the 2nd floor. So I want to plug into an electrical socket a "wireless repeater." By this, I mean a unit that is NOT directly wired to the main modem or the first-floor wireless router, but which picks up the signal and retransmits it. This would mean that anyone who goes into those corner rooms would basically be in the same situation as those who are on the first floor.
I have looked around, and many places talk about bridging or not bridging, etc. A bridge I once used abroad for a wirless connection screwed up all my other settings, and I don't want to put anyone else in my household through this. LinkSys looked promising, but the workaround to their poor service and awful manual is far too complex for me, and requires too much work for the people who want to use it.
Is there someone that can explain this clearly to me? I have looked at the D-link DWL-G710, but the details are not in the on-line manual, so I am hesitant.
Many thanks for any help.

T. T.