This is mainly for the computer-literate guys of the forum.

It's not really Nightfire-related but important for me in terms of general gaming; if moderators think it should be in with the off-topic stuff then feel free to stick it there.
I've got my new HP Pavillion tx1000z laptop (with touch screen

:grin::grin:) which I didn't specifically buy for gaming, mainly because I needed a newer, faster, dual-core laptop that didn't crash constantly. It has Vista Home Premium (some people say it's broken already

) but that's good enough for me.
However, I didn't realise how cosmically crap my integrated GPU was (nVIDIA GeForce Go 6150 in case you didn't read the title

) until I started playing elite Orange Box games like Team Fortress 2. I can't even run in 1024X768 FGS without the whole computer lagging so much at settings recommended by the engine that the game is unplayable even without being in a massive firefight, which is what TF2 is mainly all about.
I know this isn't a processor-related problem: I have 2X 1.9ghz AMD Turion64 CPUs (not as good as Intel, I know

) and with forced dual threading the game runs worse than without, which is probably due to the console command being slightly beta.
To get the game even running acceptably I have to lower the resolution to 800X600

, disable AA and AF, set the texture detail to medium (I will NOT have low because it looks so unbelivably crap it could come from a GoldSource game

) and lower shadow and water detail to the lowest. Even then, it still lags quite considerably when in a massive fight.
What I was wondering (got there in the end

) was if it was possible to replace on-board GPUs with better ones, how much it would cost, and which ones were DirectX 10 compatible. If I have Vista I better be flipping able to get DX10 or it's not worth it...
I have a feeling Tres, Ulti and people like that will know at least a bit about this.
PLEASE DO NOT tell me to go get another computer; I came here for solutions, not a name of a computer that's better that I don't have and won't be able to afford for another one and a half years because I'm still paying back the money I borrowed from my parents to be able to get my current system.
Thanks, any helpful helpful help is much appreciated.
Specs:
2X AMD Turion64 1.9ghz CPUs (=3.8ghz)
1.5gb RAM with max 128mb shared graphics memory (I have it set to 64mb at the moment because apparently that freed up more ram for the game to use)
nVIDIA GeForce Go 6150 on-board integrated GPU
Windows Vista Home Premium