Windows 7: Help finding RAM frequency for upgrade

hey guys im kinda at the end of the rope here as far as patience goes, last night i finished installing the 64 bit version of windows professional on my laptop.

i had purchased 4GB of RAM from newegg, OCZ PC2 6400 800 (2x 2GB) @ 1.8v, to make better use of the OS, i previously had 2 GB of PC2 5300s (2x 1GB) that i believe was running at 667 1.8v.

my knowledge on computers is very basic, so i thought the RAM i had purchased was fine. while still running vista i installed one of the modules bringing me up to 3 GB, it ran fine so i thought i was OK. then after i finished installing 7 i installed the second module and thats when it failed to startup correctly. i removed one and replaced it with one of the original modules and was OK again.

confused i checked online and found that i probably had purchased RAM that was running at the incorrect frequency. now i need to return it and buy a new pair, can you guys help me choose the right one?

Newegg.com - CORSAIR 4GB (2 x 2GB) 200-Pin DDR2 SO-DIMM DDR2 667 (PC2 5300) Dual Channel Kit Laptop Memory Model VS4GSDSKIT667D2 - Laptop Memory

this is what i was looking at not sure if it will work though. by the way my cpu is a core 2 duo T7200

Many feel that it is best not to mix and match, but you are right the frequency is important.

well the thing is i want to make use of the full 4 GB and the moment both new modules are installed my laptop fails to start up and goes into recovery mode. it only works if i use one of the new and one of the old modules, which is pointless because then i waste the second new one.

i want to return the ram i bought, and purchase something that is compatible, in my second post i provided a link, will that set work with my system?

my question is basically what kind of ram i should buy.

*UPDATE*

so i posted this question in yahoo answers as well and a guy gave me a link to the crucial site. i downloaded the system scanner and it told me the max memory allowed per slot was 1 GB for a total of 2GB.

as i mentioned i was temporarily running 3 GB (2GB in 1 slot and 1 GB in the other) and i had no problems. from what i read around the net, this was because the 1 GB module met the correct speed req for the motherboard and so the 2 GB unit which was supposed to be at a higher frequency was being limited to the lower frequency.

So by this logic i assumed that when i removed the 1GB unit and replaced it with the second 2GB unit, that frequency limit was no longer there and so the PC crashed.

Does this mean that i would be ok exceeding the manufacturers slot limit as long as its the correct speed?
(according to the scanner the ram in the link above is the correct speed PC2 5300)