Memory Upgrade Consult needed please...

hey guyz
this is my current specs:
P4 2.4B
ASUS P4S8X
256MB 266MHZ DDR
MSI RADEON 9800 PRO
WIN XP SP1
now that is my prob, i know my video card is okay for games, but game
just keep getting stuck sometimes (no its not a video card issue, i
get 5800 at 3DMARK03)
now i know that its comming from the memory cuz i can see that data
get in and out from my hard drive (pagefile) so i need a new stick to
keep games runs in an okay condition.
aight, i live in israel, 512mb is kinda expansive here, so i can only
afford buying an ADATA 256MB 400MHZ....
now what im asking is, if ill add it to my current memory (which i
will throw away when ill buy my next computer , probably a year or so)
could i fell some changes even if it will run at 266mhz?
i just came back from playing SOLDIERS: HEROES OF WW2, and the game
keep getting stuck all the time , and its not the only game where it
occurs..
so please answer my question, and help me
i apriciate your help.