Right/Best Value RAM for my needs (UK)

Hello, I'm looking to upgrade the memory in my laptop (HP G56). PC wizard says I currently have 2 x DDR2-SDRAM PC2-6400 (399MHz) – (DDR2-800) 2 gbs each. It says the max the system will take is 8gb so I'd like to get 2 x 4gb.

Problem is, when I search online for these I'm not sure they are suitable for a laptop and as I've never changed a laptops RAM before I am concerned I would buy the wrong thing.

Please could some one be so kind as to point me in the right direction? I think I can post what the PC wizard details are if it would help? And am looking to upgrade as finding it hard to get three levels of video to play in Sony Vegas Pro.

Many thanks

Deborah
NB: Sorry if this is in the wrong sub category, just clicked the first one as none of the options seemed relevant to me.