the presario v6000/65000 comes in multiple variations from 1gig to 8gig, with both intel and amd cpu's and lots of variation in gfx power.
while all that is being said not 1 of them is classed as a gaming grade laptop.
the chances are your system just cant cope with the demands of the game and the longer you play the more laggy it gets. its either paging out to the page file when its running out of real ram or its getting to warm and throttling.
Sounds like a heat issue. Have a good cooling fan for your laptop, it's not like a desktop which is very prone in overheating especially in gaming. You should be cautious or else you'll end up breaking your laptop.
my laptop has a AMD processor whatever that is .... and yes it does get quite hot easily for some reason i've placed video cassettes under neat so the laptop fan can cool down quicker and ive tried hoover the dust from the fan (yes it seems stupid) so now i play a game for a longer time period than before before it starts lagging again.
That laptop has a NVIDIA GeForce Go 6150 which is a bit dated for playing games so more than likely it's proble an issue with that since frame rate is going to be fairly bad regardless of how low you set the graphics.
Average expectations is about 10-17fps in a direct x9 game of the recent years on games such as Oblivion or Counter Strike Source.
However some games will let you revert back to DirectX 8 to increase rates at the cost of graphic quality by adding -dx8 in the target path.
But over all there isn't really another solution since it's a built in card.