im no expert, but wifi runs in the 2.4GHz freq, which doen't travel well through walls. you need LOS (line of sight)!! the signal is able to bounce of the walls.
at home, we can get reception through 5 walls (probably bouncing off outside wall), but only at night if it is cold outside...
I've got a site where the (WRT) router sits more-or-less centrally in the house, but in one direction there're 4 walls across and the passage wall running lengthways to get to the one PC at that end of the house. I stuck an 8dBi patch up on the end of the curtain rail and that signal never has any problems.
The other direction is worse but somehow the signal manages to make it to the office - at least for laptops that have built-in wi-fi ..and so decent antennas built into the screens. I've got the receptionist PC *up* to a "low" signal level by using a magnetic base 5dBi dipole. I can't say I'm happy with the result but it seems to be stable enough for them and seeing as I don't really have the option of the same flat panel trick here, I'll see if it's settled.
If'n it ain't I'm telling 'em to get over being tight with the budget and putting an AP in that room that's got Cat5 going back to the router so we can ALL get some peace!
If you have (access to..) a wi-fi'd laptop, why not do a Stumble from the source out to where you want connection(s) and see how bad it really is..?
HTH
-bdt
Late breaking thought: do a cost-analysis comparing boosting signals with (small, for indoor use!) antennas against just replacing regular wi-fi with MIMO tech-hardware, seeing as it's starting to become reasonably available? Personally I think it'll flat-out cost less to do the antenna thing, but that may not be your only/final/deciding criterion!