Before I upgraded last week, that's the card I was running and the resolution I was running at. I was actually able to get over 50fps when I manually switched over to DX9 in the systems.ini file. In the default DX10, I could only comfortably run at 1680x1050/medium settings. Frankly, there's no reason your brother can't just switch to that resolution on his 1920x1200 monitor. You don't have to run the game at native resolution for it to look good.
Also, don't forget that this game is highly dependent on the CPU. With his older E2180 dual core, he will likely drop below 30fps regardless of the video card: http://www.legionhardware.com/articles_pages/battlefield_bad_company_2_tuning_guide,3.html♦. Low settings may save his rig, but they really don't look too good. Trust me, it won't make a difference if he's 1920x1200 or 1280x1024 when he's at low settings.
Is low quality really that bad for you? Yea, I'll definitely tell him to force the game to run in DX9. Honestly, can you really tell the difference in quality in a fast pace FPS? I hate running games on an LCD at non-native resolution. I don't think he would appreciate it either.