I've been trying to play Halo a while now but it says my video hardware is lower than recomeneded.
These are the minimum requirements:
• Operating System: Microsoft Windows 98, Microsoft Windows Second Edition, Microsoft Windows Millennium Edition (Me), Microsoft Windows 2000, or Microsoft Windows XP.
• Computer/Processor: 733 megahertz (MHz) processor.
• DirectX: DirectX® 9.0 or later. (DirectX 9.0b is installed by Halo.)
• Memory: 128 megabytes (MB) of RAM.
• Hard Disk: 1.2 gigabytes (GB) of free hard disk space.
• Video card: 32 MB with 3D Transform and Lighting capable.
• CD: 8X.
• Sound: Sound card, speakers, or headphones with multiplayer play.
• *56.6 Kilobytes per second (KBps) modem or 10 MB network adapter. Multiplayer servers require broadband to run a server.
• *Additionally, you must have an Internet Service provider (ISP) or a Local Area Network (LAN), if you want to play multi-player games.

It says my machine info is:
1900MHz, 192 MB, 64M VIA KM400 (0x2705)

Is it possilbe to update my video card to the requirements? If you need anymore info please ask.
Thanks.

You're going to have to buy a card. It seems as if you have an onboard card. The slot you're looking for is an AGP slot. It's kind of off-set from the PCI slots and is the closest to the CPU. Also, you'd might want to invest in increasing the RAM.

I agree with legoman. Bump your RAM up to 512mb minimum and a 128mb nVidia based video card minimum. When you look at the motherboard you should have several PCI slots. They should be white. Do you have a single brown slot next to the first PCI slot closest to the processor?

AGP slots sometimes come in green. I know for a fact that Dell makes them green.

whats your OS ?

I use HP Pavillion a845w. And is there a way to increse RAM without buying a product etc.?

No, it's not possible to increase RAM without purchasing a product.