only the videocard is holding you back
For NBA 2k9, i would recommend at least an 8600GT level card or higher..
the 7300SE "tecnically" meets the minimum requirement which is SM3.0 but it has less raw power than the minimum card (GeForce 6600GT)
ok so heres my list (sorry guys, nVIDIA cards only
) of which cards will be ok (take note that this is just my estimate based on the minimum and recommended specs, I havent tried playing NBA 2k9 on other systems except my own and this list is just my educated guess)
Geforce 6200, 7100,7200, 7300GS/LEm, 8400GS (and below) = technically can but power wise, is slower than the minimum so expect bad performence
Geforce 6600, 6600GT, 7300GT (DDR3), Geforce 7600GS (DDR2),8500GT = Minimum requirement level (or a tad higher than minimum)so just take a clue as to how it would perform.At this point it doesnt matter if you have 512mb and above vRAM as these cards (and slower wont be able to make good use of it anyway)
6800 series cards, 7600GT, 8600GT, 8600GTS, 9500GT, 7900 series cards = Within the recommended card range so expect to be able to crank up a few settings here and there (depending on the resolution) at this point a 512mb card should be max, in fact if you are choosing between a 256mb 8600GT and a 512mb 8600GT I would still choose the 256mb version if there is some price difference since there wont be much of a performance advantage going from 256mb to 512mb
9600 series, 8800series,9800 series = above the recommended requirement..so depending on which card you have, you can even increase setttings like AA and AF and high resolutions
GTX series = expect constant 60fps even with 8xMSAA and 16xAF