HP is way to go if your serious about those higher end games.
I've found it to be the best bang-for-buck when it comes to stability, performance etc. There's also other gaming notebooks out there, but i'd always go for a trusted brand over something else.
anything below an 8600mGT wont do Oblivion justice(though other games should do fine), try for at least that,
i'd recc. trying for a 9600m GT, like in this HP dv5t, which starts at ~600, which is a decent upgrade in GPU
http://www.shopping.hp.com/webapp/shopping...e%20performancethere's other nice rigs that come with a Mobility 9800, but their prices go upwards of 1.5k
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If your just into Oblvion-esque games once in a while, go for an 8600M GT rig (or below if you wish) with some average specs across the board, or just look at what bob-sama recommended if your not much at all