So basically what your saying is your wireless router signal downstairs isnt strong enough to get to your PS2 upstairs ?
I have a linksys as well. All you need is a wireless signal booster. (also made by linksys) Lemme tell you....When I got mine, it increased the signal ALOT.
When I was testing it outside, I had a good signal almost a 100 yards out. Without the signal booster, it was crap.
But beware...your neighbors might be able to hop on as well.
There are plenty out there -
linksys wireless signal booster - Google Search