Wireless Woes... ...

Hello All... newbie here... i finally got my wireless card installed and the lost drivers reisntalled. the card works "ok".. i think it probably can be better. heres my dilema. i have an emachines dexsktop... T6524. and i bought with it a Buffalotech wireless LAN adapter. WLI2_PCI_G54S. when we moved into our new apt. i was not able to pick up any wireless signals. im about 50 ft away from im guessing the outside perimeter of the office's wireless connection. bummer. so i bought me a Dlink high-gain antenna. omni directional 7db. so now i can pull in all kinds of wireless connections. and i can recieve the office connection. but i can only revieve like 1 bar outta 4 in signal strength. i called my manager, who only lives about 40. he can get a great signal. now when i installed the card again. it said that it wasnt digitally signed. and i check the compatibility with windows xp. and it wasnt even listed on microsofts site. but the box says xp compatible. am i missing something here? is it just not compatible? and do i just need to go buy another card? its frustrating. i can get a signal from another neighbor, all bars. but wheni log into it, it drops to 1 bar and is slow.... please help.... It also said that a simple pci connection controller was not present. i tried to find a download or patch for it. but i guess i was not looking hard enough. any advice or direction will be greatly appreciated...

my computer:

Emachines T6524
Microstar ms-7184 motherboard
Buffalotech WLI2-PCI-G54S wireless card.
Windows XP Professional