Yes, you must resize it. Here's how:
rename it to 256km8.bin and put it in C:\bios or something you can remember
Start>run>cmd
type these commands:
cd\
cd bios
copy /b 256km8.bin + 256km8.bin 512km8.bin
exit
now you have made two copies into one 512k suitable for flashing. Obviously you can use any filename or dir you want, I'm just making it really simple.
enjoy