How to force direct x 9?

doubtful on a sony vaio made last year. That came packaged with win 7.
Regardless it's all rather moot under the crushing weight of a mobility gpu that simply can't handle the game properly.

If it's a dx 9 card and the dxversion=auto is set in the game settings file it will only run DX 9. But like Magnus said since the laptop is from last year and it was packaged with 7 I would assume that it would have a mobile graphics that's DX 10 compatible. It would be nice to see what model Sony Viao OP has so we would know for sure. He's probably also running a dual core which really screws him.

Well the best I can do for you since the op isn't around today is to tell you I just spent the last 20 minutes or so looking over vaio specs in general. They all come with ati mobility graphics current to the time of their manufacture.(at least those made in the last couple of years) That being the case it's most likely either a 4xxx or a 5xxx mobility chip.
They don't really seem to make a 'dirty cheap' model of vaio.

You can build a pc that will run BC2 for about 400 dollars if you are buying all new parts. If you have a spare case and power supply that you can use you may be able to get in at 300. But to run BC2 decently you will need a quad core processor, 4 GB of ram, and a mid-range video card. The video card will be $100, the processor/mobo will be minimum $150, and the ram will be around $40. Hard drive will be around $50. I'll post examples for you to sample:

Newegg.com - AMD Athlon II X4 645 Propus 3.1GHz 4 x 512KB L2 Cache Socket AM3 95W Quad-Core Desktop Processor ADX645WFGMBOX

Newegg.com - Seagate Barracuda 7200.12 ST3500418AS 500GB 7200 RPM 16MB Cache SATA 3.0Gb/s 3.5" Internal Hard Drive -Bare Drive

Newegg.com - ECS NGTS450-1GPI-F1 GeForce GTS 450 (Fermi) 1GB 128-bit GDDR5 PCI Express 2.0 x16 HDCP Ready SLI Support Video Card

Newegg.com - BIOSTAR N68S3+ AM3 NVIDIA MCP68S Micro ATX AMD Motherboard

Newegg.com - OCZ Gold 4GB (2 x 2GB) 240-Pin DDR3 SDRAM DDR3 1066 (PC3 8500) Desktop Memory Model OCZ3G1066LV4GK

$340 total not counting the case and power supply. If you run BC2 on a 22" display or less you will run BC2 at 60 FPS or better. You can get a case for around $40 for a budget case and the same for a psu. You'll need around a 500w supply with a solid +12v rail for your video card around 24A.

You can also check ebay and craigs list for a used system and throw a video card in it like the one above.