just give u good info. did you know some am3 processors can support am2 / am2+ mobo? of course with mobo limitation.
i ever tried to upgrade my old AM2 mobo with AMD Sempron 140 (AM3 cpu) and it works well. but AMD Phenom II is not supported because of mobo wattage output limitation.
AMD is priority of 'Compatible'. thats why i can use AM3 cpu under AM2 mobo, with some limitation of course.
I suggest you to get simple, AMD Athlon II X2 240 because Athlon 64 X2 is way outdated. plus, bit newer AM3 cpu are cheap yet powerful enough for mainstream. but i really need your mobo model. is it really support higher wattage? you can always check your mobo whether support certain cpu at manufacturer website.
but then again, whats your mobo model?
 NVidia GeForce 6150se is not really a mobo model, instead the graphic model (or chipset)