you need both parts of the 2.3 .rar files
have winrar or a similar program to unpack the .rar files
unpack them both
install them both, you start with part 1 and then part 2.
considering the size of the files you will need around 4gb free harddisk space to do this.
have bf2 patched to 1.5 before you start anything from the above
Thanks to DH for this copy&paste.