Wireless :: Signals Are Weak For Large Data?

For my network the way it is setup is one building has the 2 main servers.simple wireless router and a few laptop that connect to it. a Wii and some other devices, all of them share media etc with no issue. Internet is not a problem either.One of the servers has a PCI wireless card and connects to another network.(network2)network 2 is able to share and play all the media off the service lets say 80% of the time.It also has a different internet provider and internet connection is not a problem but the wireless signal strength is low , (2 bars) or -55 to -82 it seams to jump around at.If you try to stream or play too much media it freezes on you. or if 2 devices on network 2 try to play something it freezes as well sometimes though when the signal is good -55 ish there is no issues.There is alot of wireless traffic in the area, i cant change that.and dont really want to buy a ranger extender or something $20 is what I have for parts if anything. If I were to put a 2nd wireless card in server 2 or Server 1 even. Also both the wireless router on network 2 and the pci card on server 2 are physically as close as hey can get.