I had similar connectivity issues: my wireless Linksys router is downstairs and so on. I bought an antenna ($20..$30) and plugged it into one shoulder of the router -- no more drop-outs, though the signal upstairs is reported mostly as just good, not excellent.

I've seen a repeating device recently ($70..$90) -- the signal probably will be much stronger.

So far I can detect one more wireless network in my area (private houses) -- someone's of my neighbours. So the stronger your signal means the more attention to the connection security as well :)