In all seriousness, the 9400m really isn't that bad of a card for LAPTOPS. I play CoD4 with good results.
If you are going to get an iMac, I would seriously recommend spending the extra cash (if you have it, don't spend what you don't have) and get the gt120 or the 4750 (if you have 50 more dollars).
OR like somebody suggested, go referb and see if you can't get a good deal that way. If you aren't in too much of a hurry to purchase check the referb store every other day or so to check on new merchandise and see if there is something up your ally. I got a referb uMB and I think it is phenominal.
Good luck!
Post back and let us know what you ended up doing.